Camera adapter based optical imaging apparatus

ABSTRACT

The invention describes several embodiments of an adapter which can make use of the devices in any commercially available digital cameras to transform the digital camera into a fundus camera for inspecting the back of the eye, or into a microscope. The camera adapter is adapted to be placed between the camera device and the object. The devices in the camera being used are at least its optical source, photodetector sensor, memory, shutter and autofocus. Means in the adapter are provided to employ these devices and allow camera to operate its autofocus capability and its different color sensors. Methods of investigation of an object are also presented of using the adapter to transform the camera into an imaging instrument, where the effect of adjustments of elements inside the adapter are guided by the displaying screen of the camera.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for imaging transparentobjects in general and tissue in particular using digital cameras. Theinvention describes several adapters which can make use of the devicesin commercial digital cameras to accomplish different functions, such asa fundus camera, or as an en-face optical coherence tomography (OCT) oras a channeled spectrum (Fourier domain) optical coherence tomography(CS-OCT), or as a non-invasive dual channel optical imaging instrumentwhich can be used to provide simultaneous cross section OCT images andcompound en-face images. In microscopy, the system deliverssimultaneously cross sections from specimens and en-face orientedconfocal microscopy (CM) images. If used for imaging the retina of theeye, then the system delivers simultaneously two images, OCT crosssections from the retina and en-face oriented fundus images, of the typedelivered by a scanning laser ophthalmoscope (SLO) or a confocal SLO,i.e. the system can deliver OCT/SLO or OCT/CM dual images, depending onthe application.

PRIOR ART AND BACKGROUND OF THE INVENTION

A variety of instruments which produce depth resolved information andimaging of the eye, tissue or industrial objects are known. They involveCM and OCT principles. A general problem with all these configurationsis their large volume and high cost. This restricts their use to a fewmedical practices and research centres.

In the description which follows, reference is made primarily to thehuman eye and skin, however the invention is also applicable tomeasurements and imaging of any other objects which are sufficientlytransparent for visible or infrared light, as well as for profilometryof any object which reflects visible or infrared light. In terms ofimaging moving objects, reference is made primarily to two examples,live embryos or the retina of an eye. This has to be understood asmerely a way to help the description and not as a restriction of theapplication of the present invention. As such, where the term “embryo”or “eye” or “retina” is used, a more general transparent and scatteringobject or organ may be sought instead, the invention could equally beapplied to skin, heart, vessels, dental tissue, dental prostheses,paintings, powders and other scattering semi-transparent objects, movingor non-moving. The dual imaging aspect of the invention is especiallyuseful for moving objects.

All known imaging systems for the eye, such as fundus cameras, slitcameras, SLO and OCT systems as well as imaging systems for skin, othertissue, profilometry use an optical source, scanners, some optics and areader, in the form of photodetector devices or 1D or 2D photodetectorarrays.

However, all these systems are inaccessible to most of the small medicalpractices and small businesses due to their high cost. Some usesophisticated optical sources, such as femtosecond lasers pulsed or CWlasers, specialized sources such as superluminiscent diodes (SLD). Theseoptical imaging systems also use specialized 1D and 2D photodetectorarrays, or many pixels, high dynamic CCD or CMOS cameras, of high cost.

The implementation of such systems on specialized chin rests for imagingthe eye or microscopy on highly specialised frames lead to a furtherincrease in their price.

There are instances when home, cross section or en-face images would beneeded of translucent objects, such as nails, sheets of paper, objectsof ceramics or porcelain, etc. A 1D profile of reflectivity in theanterior chamber of the eye could be used to evaluate the sugar contenteliminating the need of the current invasive measurement methods using adrop of blood. The bulky format of available OCT systems and their costprevent OCT technology from replacing invasive methods, or penetratingthe consumer market, to the level and extent of electrical appliances.High skills are required to operate such OCT systems, at the level of awell educated Physicist, engineer or medical practitioner. They aresophisticated and complex and cannot be handled in the way a PC or anelectrical appliance is used by any consumer.

Due to the reasons mentioned above, it is hard to imagine that suchsophisticated imaging systems would have a wide spread in thecountryside and small towns where authorities struggle in ensuringprovision of even basic medical devices. Also, small companies cannotafford to purchase such systems for profilometry or topography, distancemeasurement, or correlation measurements due to their high cost.

In the battle field, ophthalmologists need OCT systems to evaluate eyedamage. Art conservationist need OCT systems in harsh environments, ineither very hot conditions or very cold. Underwater inspection of relicsby conservationists or salvage teams is another example where portableand compact high resolution instruments are needed. The bulky systemsknown today cannot be easily made transportable or adapted for harshconditions.

Therefore, a need exists for more compact high depth resolutionmeasurement and imaging systems, portable and of much lower cost toallow the spread of confocal microscopy technology and of OCT technologyto satisfy the needs of ordinary people without resorting to specializedequipment or advice, or to satisfy the needs of specialists working inharsh weather conditions or difficult environment and to be used bysmall practices in diagnostic as well as by small companies in industry.

There are also known imaging and measurement instruments usingmonochrome high performance cameras. The imaging of moving organs orobjects or fast evolving phenomena is often difficult due to the timerequired to collect repetitive data for different values ofpolarisation, wavelength or angular incidence for polarisation,spectroscopic and speckle reduction imaging respectively.

Therefore a need exists to speed up the acquisition by conveniently andadvantageously employing the novel features available in modern digitalcameras.

A form of spectral domain OCT, called channeled spectrum (CS) of Fourierdomain OCT is based on reading the channeled spectrum at the output ofan interferometer using a spectrometer, as described in “DisplacementSensor Using Channeled Spectrum Dispersed on a Linear CCD Array”, by S.Taplin, A. Gh. Podoleanu, D. J. Webb, D. A. Jackson, published inElectron. Lett. 29, No. 10, (1993), pp. 896-897 and in “ChanneledSpectrum Liquid Refractometer”, by A. Gh. Podoleanu S. Taplin, D. J.Webb, D. A. Jackson, published in Rev. Sci. Instr., vol. 64, No. 10, pp.3028-9, (1993). By adding a transversal scanning head to theconfiguration described in these two papers, OCT functionality isachieved. However, such methods produce B-scan OCT images only. It willbe desirable to have an en-face image to guide the B-scan acquisition ofmoving embryos, organs or any other moving samples. It will also beuseful to see the eye fundus when cross-sectioning the retina. Fourierdomain optical coherence tomography systems are based on aninterferometer whose spectrum is read by a linear CCD array. Increase inthe speed and dynamic range of digital linear cameras allowed progressin this field. Cameras with 2048 pixels which could be read at more than100 kHz line rate are now available. SLR cameras with more than1000×1000 pixels and with a 10 microsecond acquisition times are alsoavailable, which shows that the performance of commercially availablecameras improved to the level of scientific more expensive cameras.

OCT has mainly evolved in the direction of producing cross-sectionalimages, most commonly perpendicular to the plane of images delivered bya microscope or by a SLO. The depth resolution in SLO is 30-100 μmcoarser than that in OCT while the transversal resolution in OCT isaffected by random interference effects from different scatteringcenters (speckle), inexistent in SLO images. Therefore, there is scopein combining SLO with OCT. Different avenues have been evaluated, toprovide an SLO using CS-OCT systems. The main motivation for OCT/SLOcombination is to provide orientation to the OCT channel. Crucial forthe operation is pixel to pixel correspondence between the two channels,OCT and SLO, which can only be ensured if both channels share the sametransverse scanner to scan the beam across the eye.

An equivalent SLO image can be generated from several OCT B-scans. Then,by software means, an SLO image can be inferred without using abeamsplitter or a separate confocal receiver. After a 3D data setacquisition, a confocal microscopy image of the embryo (or an SLO-likeimage of the retina is generated) and then the B-scan OCT images can berevisited through the 3D data set with simultaneous display of thesynthesized CM (or SLO) image. SLO-like image cane be inferred fromB-scans using CS-OCT systems, as reported in Hong, Y., Makita, S.,Yamanari, M., Miura, M., Kim, S., Yatagai, T., Yasuno, Y 2007,“Three-dimensional visualization of choroidal vessels by using standardand ultra-high resolution scattering optical coherence angiography”,published in Opt. Express 15, 7538-7550 or by Jiao, SI., Wu, C. Y.,Knighton, R. W., Gregori, G., Puliafito, C. A., 2006, “Registration ofhigh-density cross sectional images to the fundus image inspectral-domain ophthalmic optical coherence tomography”, Published inOptics Express 14, 3368-3376.

The main advantage of the spectral OCT method relies on its high speedwhich allows collection of a large data set of pixels. With a highdensity of 65536 A-scans, obtained at 29 kHz, 2.25 s are required forthe whole volume. The transversal resolution along the synthesis axis ofthe SLO image is given by the spatial sampling, i.e. by the lateralinterval from a B-scan to the next B-scan along a rectangular directionto that contained in the B-scan image. Such SLO-like C-scan imagesexhibit the normal transversal resolution (15-20 μm) along the B-scanlateral coordinate (X) and the coarse sampling interval, along thelateral rectangular direction (Y). For instance, let us say that theimage is from an area of 4 mm×4 mm on the retina of 512×128 pixels. Thismeans that the Y-pixel size is 4 mm/128=31 μm. This size could bereduced by increasing the acquisition time in order to capture moreB-scan images but would also result in more cumulated artefacts due tomovement. If correction is made for the large transversal pixel sizealong the Y-axis, to achieve the normal pixel size of 15 μm in anaberrated eye, acquisition time would increase to over 4.5 s.

The disadvantage of this method is that the CM (or the en-face fundusimage) is generated after (i) acquisition is complete and (ii) softwareevaluation, both steps requiring some time. As another disadvantage, aspresented above, the transversal resolution along the sampling directionof B-scan repetition is coarser than the transversal resolution alongthe lateral direction in the FD-OCT image.

Other possibility is to produce an en-face cumulated image (microscopyor SLO) and then switch the system to acquire a fast B-scan OCT image.The operation can be sequential and not simultaneous because thereference beam has to be blocked when acquiring the CM (or SLO) image,otherwise the reference beam saturates the CM (SLO) channel or producesnoise in this channel.

Another possibility is to divert light form the object towards aseparate splitter, as disclosed in the U.S. Pat. No. 5,975,697 for atime domain OCT and for a CS-OCT system in US2008/0088852 A1 by J.Rogers and M. Hathaway. This method however reduces the amount of lightused for generating the OCT images.

Therefore, the present invention seeks to overcome the abovedisadvantages, providing configurations and methods of operation,characterized by simultaneous parallel acquisition of the OCTinformation and of microscopy (eye fundus) information.

SUMMARY OF THE INVENTION

The present invention solves the above problems by means of methods andseveral configurations of apparatuses devised around commerciallyavailable CCD cameras.

In a particular aspect, there is provided an adapter as set out in claim1 and a system as set out in claim 8.

In preferred embodiments, the methods and apparatuses make use of theelements which equip any commercial digital photo camera, aphotodetector array, a flash optical source, a guiding beam forautomatic focus, shutter button, diaphragm control, shutter timeadjustment and interface optics which transfer the light from the objectimaged to the photodetector array including the automatic focus,electronic interface to transfer the image or images stored in thephotodetector array to a separate computing system and the memory card.

The present application describes methods and devices to produce imagessimilar to those produced by sophisticated and dedicated fundus camerasor OCT systems when imaging the eye and methods and devices to produceimages similar to those produced by sophisticated and dedicatedmicroscopes or OCT systems when imaging skin, other types of tissue,industrial objects or profilometry instruments. The applicationtherefore describes adapters to host conventional commercially availablecameras and allow the elements above equipping any camera to be usedconveniently to accomplish several operation functions. The adaptershave to perform functions required by the optical principle involved aswell as to adapt the existing elements to commercially available camerasto best accomplish functions to which they have not initially beendesigned for, while at the same time minimize the disadvantages of theoriginal design which optimised the camera for its main function,photography. For instance, optical sources in photography are flashsources, they do not emit a continuous wave (CW) generally used in highresolution imaging. One the other hand, the IR beam, emits CW but hasmuch lower power. Both sources, the flash and the IR beam are divergent.The flash may also be of different shapes and exhibit narrow spectralspikes. As another disadvantage, the photodetector array and the sourceare placed within the same compact spatial block and assembled toaccomplish photography, a different function than that envisaged by thepresent application.

The present application presents devices and methods to take advantageof the specificity of elements designed for digital photography. Forinstance, the advancement in the timing of flashes towards shorter timebursts suits ideally the needs for OCT, where to avoid the washout offringes, ms and sub-ms duration of fringe readout is required.

The present application also describes methods and devices to producedepth resolved information and images using colour cameras which can beextended to specialised systems for speed of operation and versatility.

The application will describe methods and devices to image differentobjects using principles of microscopy or fundus cameras, or OCT,methods and devices which can be implemented using the elements in anycommercially available cameras, including the possibility of usingexternal optical sources, normally associated with photography, such aspowerful controllable flashes, USB or TTL.

In keeping with the invention, a much lower cost solution is providedwhich employs the elements in any commercially available camera toachieve different functionality. In order to make use of such elements,the present invention provides different versions of adapters whichtransform a camera (or suits several cameras to be transformed) intospecialized imaging instruments.

Thus, in a first aspect the invention provides an adapter whichtransforms a conventional commercial camera into an en-face OCT imagingsystems with demodulation based on known principles of Hilberttransformation or phase shifting interferometry. Two or three imageshave to be at least collected in order to obtain an en-face OCT image (aC-scan OCT image). These can be acquired for each press of the shutter.Alternatively, by using the rapid fire of several flashes, featureequipping modern cameras or separate flash optical sources, severalphase steps are created and for each step an image is acquired with allsteps triggered by pressing the shutter once only.

In a second aspect, the three colour sensitive parts of the sensor areused to provide the three phase shifts for one data acquisition step ofan en-face OCT image (C-scan).

In a third aspect, the three colour sensitive parts of the photodetectorsensor are used to provide a specific quantity OCT en-face imaging byproducing an en-face OCT image for each spectral optical band asdetermined by the spectral sensitivity of the sensor and the spectralemission of the light source, where the specific quantity could beeither wavelength for spectroscopic analysis, polarisation, angularincidence for speckle reduction or step delay for range extension andcurvature of curved objects such as the cornea.

In a fourth aspect, the invention provides an adapter which transforms aconventional commercial camera into a longitudinal OCT system, where adepth profile, i.e. an A-scan can be obtained using CS-OCT. This couldbe used for thickness evaluation of thin translucent objects, such asthe cornea and paper, to determine the length of the anterior chamber ineyes to sense variations in the glucose level in blood, could be used totrace scratches for forensic analysis, etc.

In a fifth aspect, the invention provides for an enhanced version of theabove where the same line of pixels in a colour digital camera are usedto provide simultaneously three A-scans for the three spectral bands ofthe three sensitive parts of the sensor.

In a sixth aspect, the invention provides for an adapter which uses theCS-OCT principle, where the light from a low coherence interferometer isdispersed or diffracted in a spectrometer type set-up and the result islaunched to the sensor array in a camera to produce an A-scanreflectivity profile from the object to be measured, or by using lineillumination, to generate a cross section image, i.e. a B-scan OCTimage.

In a seventh aspect the invention discloses an adapter which uses theCS-OCT principle and a transversal scanner to generate either a crosssection image, i.e. a B-scan OCT image (a lateral x depth map) or tocollect volume data from a sample by repeating the acquisition ofseveral B-scan OCT images.

In an eighth aspect, the present invention relates to an adapter whichis based on channeled spectrum low coherence interferometer where inorder to eliminate the mirror terms in CS-OCT, the reference beam in theinterferometer is shifted laterally relatively in relation to the objectbeam before hitting the spectrometer.

In a ninth aspect, the present invention relates to an adapter which isbased on channeled spectrum low coherence interferometer where in orderto avoid saturation of a separate confocal receiver due to the referencebeam, the reference beam in the interferometer is shifted laterallyrelatively in relation to the object beam before hitting thespectrometer. The dispersing element in the spectrometer may utilizediffraction or dispersion, i.e. it may employ a diffraction grating or aprism to angularly deflect the rays according to their wavelength orfrequency. When a diffraction grating is used, the two interferometerbeams, object and reference are slightly laterally shifted and the lightin the zero order from the object beam is sent towards the CM (SLO)channel and the light in higher diffraction orders serves producing theA-scan OCT image by interference on the sensor array. When using aprism, reflection from one facet of the prism is used to divert lightfrom the object beam towards a CM (SLO) receiver while the two beams,object and reference, are laterally shifted, then suffer dispersion andthen interfere on the sensor array. The invention uses an optimisedlateral shift of the two beams. The shift value is a minimum to ensurethat no reference beam penetrates the CM (SLO) aperture in either caseof the dispersing element mentioned above, diffraction grating or prism,and not too large to avoid the decrease in the spectrometer sensitivitydue to the spectrometer resolution. In this way, simultaneousmeasurement of intensity of light using the confocal receiver with theA-scan OCT provided by the sensor array is made possible. The adaptermay also include a device or devices for phase modulation or frequencyshifting to provide means for full range CS-OCT, where the mirror termsare eliminated by constructing the complex Fourier transformation.

In this aspect, variations are admitted in the form of: (i) using a 2Dtransversal scanner to scan a flying spot over the object to be measuredor imaged, with the confocal receiver employing a point photodetectorand (ii) using a 1D transversal scanner to scan an illuminating lineover the object, in which case the confocal receiver employs another 2Dcamera utilised as a line camera, or the confocal receiver uses a linecamera, where in all cases such system provides simultaneously anen-face image (microscopy or eye fundus) with volume collection ofmultiple B-scans OCT images,

In a tenth aspect, the invention provides an optical configuration withminimal losses where a 50/50 beamsplitter is used to create two shiftedobject and reference beams for two cameras which are assembled in theadapter to operate in CS-OCT regime.

The lateral shift of the two beams can be customised for two possiblegoals: (i) to eliminate the noise due to autocorrelation terms in eacharm of the OCT interferometer, eliminate the zero frequency and themirror terms which lead to ghost images for OPD values of the samemodulus but opposite sign; (ii) by adding confocal receivers, where thetwo object beams, output of the beamsplitter are subject to no spectralanalysis and are summed up in the confocal receivers, while the objectand reference beams are spectrally analysed by each spectrometer andtheir results is subtracted, and where the lateral shift of the objectand reference beams prior to the 50/50 beamsplitter is just sufficientto displace the reference beam out of the input apertures of the twoconfocal receivers. In this aspect, variations are admitted in the formof: (i) using a 2D transversal scanner to scan a flying spot over theobject to be measured or imaged, with the two confocal receiversemploying point photodetectors and (ii) using a 1D transversal scannerto scan an illuminating line over the object, in which case the confocalreceivers use two other 2D cameras utilised as line cameras, or theconfocal receivers use line cameras, where in either case such systemprovides simultaneously an en-face image (microscopy or eye fundus) withvolume collection of multiple B-scans OCT images.

In an eleventh aspect, the invention provides for an adapter where thethree colour sensitive parts of the photodetector sensor are used toprovide a specific quantity longitudinal OCT imaging (A-scan or B-scan)by producing a longitudinal OCT image (A-scan or B-scan) for eachspectral optical band as determined by the spectral sensitivity of thesensor and the spectral emission of the light source, where the specificquantity could be either wavelength for spectroscopic analysis,polarisation or angular incidence for speckle reduction.

In an twelve aspect of the present invention, there is provided anadapter which transforms a digital camera into a fundus camera.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are believed to be characteristic of thepresent invention, as to its structure, organization, use and method ofoperation, together with further objectives and advantages thereof, willbe better understood from the following drawings in which presentlypreferred embodiments of the invention will now be illustrated by way ofexample.

It is expressly understood, however, that the drawings are for thepurpose of illustration and description only and are not intended as adefinition of the limits of the invention. Other features of the presentinvention, as well as other objects and advantages attendant thereto,are set forth in the following description and the accompanying drawingsin which like reference numerals depict like elements. Accordingly,various embodiments of the optical imaging apparatus of the presentinvention will now be described by reference to the following drawingswherein:

FIG. 1 shows a first embodiment of the present invention where adedicated adapter uses a commercially available camera to collect eyefundus images.

FIG. 2 shows a second embodiment of the present invention where adedicated adapter uses a commercially available camera to acquireen-face OCT images from a fixed depth within the object.

FIG. 3 shows an embodiment of the OPD adjustment block to operate inconjunction with a colour camera.

FIG. 4 shows a third embodiment of the present invention where adedicated adapter uses a commercially available camera in a CS-OCTset-up to obtain an A-scan or a B-scan OCT image from the object.

FIG. 5 shows a fourth embodiment of the present invention where twocameras are used in a balance detection CS-OCT set-up to obtain lowernoise or mirror free cross section OCT images from the object.

FIG. 6 shows a fifth embodiment of the present invention to performCS-OCT using a multiplexer to superpose all spectral bands on the samepixels of the photodetector array.

FIG. 7 shows a sixth embodiment of the present invention which providessimultaneously two measurements, low coherence interferometry andintensity or two images, an OCT image and a microscopy or SLO image.

FIG. 8 discloses a seventh embodiment of the present invention whichprovides a more efficient and less noisy equivalent of the embodiment inFIG. 7.

FIG. 9 describes an embodiment where the main splitter is in fibre andlight from the optical source is confined to fibre.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various features of the present invention, as well as other objects andadvantages attendant thereto, are set forth in the following descriptionand the accompanying drawings in which like reference numerals depictlike elements.

1. FUNDUS CAMERA

A fundus camera for imaging the retina, as well as OCT imagers involveand make use of techniques known in the art, to produce images using CCDcameras or arrays of photodetectors. They use optical sources andspecial interfaces to image the retina and transfer the reflected lightinto a 2D pattern projected on the CCD array. By adding a reference beamto the beam conveying the 2D information carried by the object beamreflected from the target, a full field or a coherence radar OCT systemis obtained. In order to adjust the position in depth where the image iscollected from, the OCT systems have means for longitudinal scanning ofthe reference path length, have means for controlling the phase andpolarization in order to maximize the interference signal and have meansto display images. These systems generate C-scan images, i.e. constantdepth images with thickness determined by the coherence length of theoptical source employed. In a Cartesian coordinate system, where the x-yplane is the plane in which en-face images lie, and the z axisrepresents the depth direction, B-scans are longitudinal sections inplanes such as x-z or y-z planes containing the z axis, and C-scans aretransverse sections in planes parallel to the x-y plane.

By spectral decomposition of the light output from the interferometer,depth information is encoded in the modulation of the spectrum observedand a linear CCD camera can provide in this way, with no mechanicalscanning, a reflectivity profile in depth, an A-scan. However these linecameras are expensive and the cost of camera Link cards and associatedI/O boards adds to the high cost. The systems are also assembled onspecialised chin rests or microscopes, are bulky and non-transportable.

Optical sources and photodetector arrays equip any commerciallyavailable digital photo cameras. As they are mass produced, their costis much lower than those of optical sources and CCD cameras used in theknown reports so far.

The present invention discloses different adapters which can transform aconventional commercial camera into a versatile, multi-functional highresolution single or dual channel measurement or imaging instrument.

As shown in FIG. 1, a commercially available camera, 1, has thefollowing elements, an objective, 2, equipped with focusing optics,usually a group of lenses, 21, a 2D photodetector array, 3, an opticalsource, 4, usually a flash lamp, electronics interface block, 5, tohandle the digital data equipped with a connector, usually a USBconnector, to connect the camera to a PC and an infrared (IR) source foraiding the focus, 6. The camera is also equipped with a viewer, 7, toobserve the object to be imaged, 100. This in FIG. 1 is the retina of anhuman or animal eye.

To acquire images from the object 100, an adapter, 10 is used accordingto the invention. The adapter contains an optical splitter, shown in theform of a plate beam-splitter, 25, in FIG. 1. Light from the objectreturns to the camera 1 via the splitter 25. To illuminate the object100 in FIG. 1, using the flash lamp, 4, the adapter produces acollimated beam using focusing elements, 11 a and 11 b and a reflector,12. Similarly, to convey the beam from the IR source 6, focusingelements 11 a′ and 11 b′ and a reflector 12′ are used. This is requiredbecause usually, the flash lamps in cameras produce divergent beams. Thefocusing elements 11 a and 11 b and 11 a′ and 11 b′ produce collimatedbeams of 3-6 mm, preferably 3 mm to avoid the need of dilating thepupil. Spatial filtering is achieved with pinholes 18 and 18′.

Optical spectral filters 19 and 19′ are placed in the beams of the flashsource 4 and IR 6 to narrow their band to improve the accuracy ofspectroscopic analysis. The adapter and digital camera and eventuallyanother optical source, 4′, are secured mechanically via a solidminiature support 90.

Light reflected by the optical splitter 25 passes through the eye pupiland anterior chamber, 100′, towards the retina 100. An intermediatefocusing element, 13, is required to fit the retina image on the 2Dphotodetector array 3. The elements 13 and the camera focusing element21 are used jointly to produce a focused image of the retina on the 2Dphotodetector array 3, when is either illuminated by the flash lamp 4 orby the IR source 6. Alternatively, the camera can use its electronicsblock 5 to adjust the focus automatically using the IR beam as wouldnormally do without the adapter 10.

Light from the anterior chamber may reflect towards the camera 1 andsaturate the array 3. To avoid this, light is linearly polarized usingpolarisers 14 and 14′ and then sent via quarter wave plates 15 and 15′.Polarised light with orientation at 45 degrees from the waveplate axeswill be transformed into circular polarized light. When light returnsfrom the anterior chamber, the circular polarized light changeshandedness and when going through the quarter wave plate 15″ acquires alinear polarized direction perpendicular to that generated by thepolarizer 14. The linear polarizer 14″ oriented at 90 degrees eliminatesthe specular reflection from the anterior chamber. If the arrangement ofwave-plates 15, 15′ and 15″ and polarizers 14, 14′ and 14″ are used,this has the disadvantage also of producing a polarization sensitiveimage from the eye fundus. Therefore, elements 15, 15′ and 15″ and 14,14′ and 14″ may not be used all the time. Possible elimination of theanterior chamber reflection could be implemented in a different way bysending the beams from the optical sources, 4 and 6 slightly off-axiswhile maintaining the array 3 on-axis. It is also possible to shift thearray 3 off-axis and use the beams from the optical sources 4 and 6on-axis.

It should be obvious for those skilled in the art that the elements 14,15, 19 as well as 14′, 15′ and 19′ could be placed anywhere in the beamfrom the flash 4 or from the IR beam 6 respectively.

If the power from the flash 4 is of too large power for the eye, then anattenuator 16 is inserted into the beam from the flash.

In order to adjust the focus on the retina, depending on the cameraused, different procedures are feasible. If the camera is equipped withautomatic focus only, then the axial position of the lens 13 is manuallyadjusted in different positions by actuating on the translation stage 17and the IR beam 6 is used, checking the image of the retina on thecamera monitor 8. Alternatively, if the IR beam does not have sufficientpower, several images are collected and their sharpness checked on themonitor 8 or on the PC, 50, connected to the electronics block 5.

If the camera can be set on manual focus, then the user can actuate onboth the camera focus control set on manual via block 5, which controlsthe objective lens 21, and onto the stage 17 to move the focusingelement 13, in order to obtain a sharp image under illumination providedby the IR beam 6. If the IR beam 6 is of insufficient optical power,then several images can be collected and the sharpness checked on themonitor 8.

Alternatively, the integration time of the camera can be increased toenhance its sensitivity and become able to employ the IR beam to producea good signal to noise ratio image from the retina. This is a commonfeature for most of the commercially available cameras which can be usedto enhance their sensitivity considerably.

Images are stored on the internal memory card 51, or sent directly tothe PC 50 via the connecting cable or wireless connection such as bluetooth, 55.

The focusing elements and processing light elements of the opticalsources of the conventional camera 1 are placed on adjustable supportsto allow spatial lateral and height adjustment to accommodate differentcameras on the market and be placed at corresponding distances from thecamera axis to intercept the beams out of sources 4 and 6. Commerciallyavailable cameras present different formats, some cameras are ultra-slimand small, others at the higher performance end are larger. Mechanicaladjustments could be provided in two or three or more versions to fitsuch variations from vendor to vendor and this will be indicated on theversion of adapter 10 to be fabricated.

Spectroscopic Imaging

Spectroscopic analysis can be performed by collecting several images ofthe retina for each press of the shutter button 9 for a different filter19. The filter can be changed manually. Alternatively, a micro-filterwheel can be used or an electrical controlled filter whose centralwavelength band is advanced for each press of the shutter. To do this, aphotodetector with driver 26 is used to advance the filter position inthe spectral filter 19 via a counter for n filter steps, 138, where thecontrol commands are sent along the line 128.

Details

The object may be the retina of a human eye or animal and the adapter isused to convey light from the retina towards the said commerciallyavailable camera through the eye pupil and the said source interfaceoptics conveys light towards the retina through the eye pupil and wherethe said source optics interface and the adapter use waveplates andpolarizers to operate like optical isolators to reduce the reflectionsfrom the anterior chamber of the eye.

The digital camera may be a colour camera where pixels in the saidphotodetected array are sensitive to three colours, r, g, b and wherethe flash source interface optics is equipped with a spectral filterunit to select three optical windows, r, g, b, each centred on themaximum of sensitivity of the colour segments r, g, b in thephotodetector sensor, out of the spectral output of the flash source ofthe digital camera.

The camera may be equipped with an accessory mount for handling theadapter and the camera in front of the object.

The said accessory mount may be equipped with means to be attached tothe object.

The accessory mount may be equipped with means to be held by an user.

The accessory mount may be equipped with means to allow stable manualscanning of the object by moving the adapter laterally and axially inrespect to the object.

2. TIME DOMAIN EN-FACE OCT

FIG. 2 describes a second embodiment of the present invention. Theadapter here is designed to transform the camera into an en-face OCTsystem. A low coherence interferometer is assembled using the flash 4,or the IR beam 6, as a low coherence source. Optical spectral filter 19may be equipped with notch filters to reject narrow spikes of the flashsource which deteriorate the correlation function of the interferometer.An optical splitter 25 divides the beams from the optical source, 4 or 6or both into an object beam and a reference beam in a Michelsoninterferometer. In addition to the embodiment in FIG. 1, a referencepath is added to create a reference beam to interfere with the objectbeam from the object 100. The reference beam is reflected by an opticalpath difference (OPD) adjusting block, 110. This is used to adjust theOPD value, i.e. the depth where the en-face image will be acquired fromthe object 100, considered the cornea or skin in the example, with lightfocused by a focusing element 41. It should be obvious for those skilledin the art that the embodiment could equally be used for imaging theretina if a suitable optical interface is added or the role of theconvergent element 41 is accomplished by the eye lens.

Focus is achieved by using the manual or automatic focusing adjustmentof the digital camera which moves objective 2 or using a supplementarytranslation stage 17 to move the focusing element 41.

The other function of the block 110 is image demodulation by inducingoptical path modulation. In order to create an en-face image, accordingto principles of phase shifting interferometry, at least three framesneed to be collected for three different OPD values, therefore the block110 has to change the OPD in steps of λ/3, where λ is the centralwavelength of the optical spectrum of the source used, 4 or 6.Therefore, an optical path modulator, 111 is used. In order to alter theOPD, different possibilities exist, as illustrated in FIG. 2. Anelectro-optic modulator or a magneto-optic modulator, 111, withassociated polarizer elements can be used under electrical signalcontrol, as a phase modulator. Another possibility is for a mechanicaloscillator, based on a piezostrictive or magnetostrictive element, 114,which suffers dimensional changes under electrical signal, to move themirror 113 which returns the reference beam back to the optical splitter25. If the adapter transforms the digital camera 1 into a microscope,then a Linnik configuration can be implemented in which case asupplementary converging element is used, 46 (preferably of the samefocus power as that used in the object path, 41) in front of the mirror113.

Alternatively, the block 110 can be assembled as a spectral scanningdelay line. A spectral delay line uses a diffraction grating, a lens anda galvanometer scanner. The linear variation of phase versus opticalfrequency is introduced by tilting the galvanometer mirror behind alens, where the galvanometer mirror is situated in the Fourier plane ofthe lens.

The adapter and the camera can be moved laterally along a slidingmechanism 91 to collect images or perform measurements from differentparts of the object 100. The support 91 is also equipped with straps andadapting means which are customised to different types of objects,cornea of the human eye, vertical mount for imaging cornea of animals,microscope mounts for histology specimens or protecting supports in caseobjects of art are imaged with proximity sensors or other means to avoidcontact, or other supporting means for used underwater or in harshconditions. These adapting means are designed as extras and could bebought as accessories to the adapter to customise the adapter to aparticular application.

An accessory mount can be devised to secure the adapter on the object,such as a patient when imaging skin.

An accessory mount can be devised to secure the adapter on the hands ofthe user when imaging paintings or working underwater.

The sliding mechanism can be provided with scales for accurate stepsalong rectangular directions and locking devices. The adapter carryingthe camera is moved laterally, locked in place and then an acquisitionprocess is triggered by the PC 50 or by pressing the shutter button 9.

2.1. Phase Shifting Interferometry

The camera is required to flash at least two or three times to collecttwo or three images for different OPD values. Some cameras can providequick flashing, at least two or three are required, in a rapid firesequence after the press of the shutter button 9. In this case, two orthree frames are acquired and an en-face OCT image is produced in the PC50 after downloading the two or three frames from the storage card 51 orafter direct download.

The generation in succession of two, three or more electrical spikes tostep the phase in the OPD adjustment block 110 is controlled by theelectronics block 5 in the camera 1 along line 125.

In case the camera does not provide an electrical signal synchronouswith the flash 4 nor with the shutter button, 9, then the adapter takesthis role. To this goal, the adapter is equipped with a photodetectorand spike shaper, 26, which under the control of the flash beam from thesource 4, delivers a trigger signal via line 27, which actuates onto theOPD adjustment block, 110. This controls either the mechanicaloscillator or piezo 114 or the optical modulator 111, which here is usedas a phase modulator. Alternatively, the line 27 can supply spikes tothe PC 50 which can actuate onto the block 110 via line 125.

To obtain another en-face image from a different depth from within theobject, eye, skin, teeth or painting, the reference reflector positionis changed accordingly by moving the translation stage 115, which holdsthe mirror 113.

Alternatively, the translation stage 115 could be equipped with amicro-motorised stage and controlled via an electronic interface alongthe line 117. If the block 110 uses a spectral scanning delay line asexplained above, then the line 117 actuates on the galvo-scanner in thescanning delay line.

Intuitively, if a spectral scanning delay line is used, then threeelements are required: (i) a galvo-scanner which takes the position ofthe mirror 113, (ii) a focusing element, a lens or a curved mirror whichtakes the place of the mirror 112 and (iii) a diffraction grating whichtakes place of the modulator 111.

The flash 4 or the IR beam 6 may have too large a bandwidth, whichdetermines a too short coherence length. This leads to a too thin OCTen-face image. This may be altered by using a narrow spectral filter, 19and 19′, in front of the sources 4 and 6 respectively. This may alsoimprove the tolerance of the interferometer in the adapter todispersion. This may also be required for the phase shifting methodefficiency. It is also known that the modulation efficiency ofelectro-optics and magneto-optic modulators depend on wavelength, andtherefore a spectral filter, 19 and 19′ may be found useful.

Shutter times of ms and sub-ms as well as flash duration of sub ms areideal for avoidance of fringe washout. The transfer of images to memoryor card 51 may be long, however the camera shutter can be opened withcurrently available technology for ms or sub-ms time to acquire a highvisibility fringe signal.

Another function of filter 19 is that of rejecting or attenuating thenarrow spikes in the flash emission, known being that these reduce thedepth resolution in OCT. This is necessary when the flash lamp usesgases, such as the Argon or Krypton flash lamps. However, modern flashlamps use high power LEDs which exhibit an ideal white large bandspectrum for low coherence interferometry measurements and OCT imaging.

In case the flash lamp is made from three powerful LEDs on the threefundamental colours, then the pinhole 18 is replaced by three differentpinholes, one for each colour source, situated in a plane perpendicularon the optic axis starting from the centre of the flash 4. This willlead to deviation of colour beams within the object beam and deviationof the colour images on the sensor. This may be tolerated on the expenseof larger transversal pixel size. As explained below, this may betolerated in the angular compounding application for speckle reduction.Additionally, the three images could be shifted after acquisition forsuperposition.

Alternatively, the beams from the three point sources corresponding tothe three pinholes could be brought to coincidence using micro dichroicfilters and splitters using principles used in the construction of theblock 110 in FIG. 3 or of the multiplexor 140 in FIG. 6.

In some of the applications described here where the colour parts of thesensor are used, the optical source is conditioned to launch its largespectrum into three spectral bands of suitable width centred onconveniently chosen central wavelength as to ensure a good cross talkbetween the colour parts of each pixel. Depth resolutions in the rangeof 10-20 microns are achievable with bandwidths in the range of 10-30nm. Therefore, for good cross-talk, the width of the three spectra willbe limited to let us say 20 nm and separated by 20 nm, this gives a 100nm emission spectrum. The flash sources are sufficiently strong andrequire attenuation for safety. Creating gaps in the spectra between thecolour components will lead to the necessary power reduction. Flashsources cover more than 200 nm band in the spectrum and the division oftheir spectrum in three bands of 20 nm each is possible. To ensuresimilar depth resolution, the filters to trim the spectrum could beconveniently adjusted to

$\begin{matrix}{\frac{\lambda_{r}^{2}}{\Delta \; \lambda_{r}} \approx \frac{\lambda_{g}^{2}}{\Delta \; \lambda_{g}} \approx \frac{\lambda_{b}^{2}}{\Delta \; \lambda_{b}}} & (1)\end{matrix}$

where λ_(r), λ_(g), λ_(b) are the central wavelengths of the three bandsand the Δλ₂, Δλ_(g), Δλ_(b) are the bandwidths of the three peaks leftin the source emission spectrum after spectral filtration.2.2. Collecting a Stack of En-Face OCT Images from Different Depths.

Different procedures are possible, depending on the camera. If thecamera is equipped with an input which accepts pulses for controllingthe moment when images are taken (external shutter), or if it has aremote control for the time of image taking, or if it is equipped withan interface, normally a USB connector, then the PC 50 takes control ofthe acquisition. For each required depth, via the control line 117, aprogram in the PC 50 controls the OPD in the interferometer by movingthe stage 115 or via line 125 controls either the vibrator or piezo 114or the phase modulator 111 or both. If the role of subwavelength shiftsis left to the piezo 114 and phase modulator 111, then the stage 115 isused for bigger steps, D. The stage 115 is moved in steps, D, comparablewith the coherence length of the optical source, 4 or 6, estimated as afew microns. For example, the block 110 is stepped in incremental stepsof D=20 microns, and for each such step, the OPD is changed in smallsteps of λ/n using the piezo 114 or/and phase modulator 111, with atypical value for n=3. For n=3, the signal at each pixel is obtainedfrom three values, I₁, I₂ and I₃ of the same pixel obtained for the 3steps by:

s=√{square root over ((I ₁ −I ₂)²+(I ₁ −I ₃)²+(I ₂ −I ₃)²)}{square rootover ((I ₁ −I ₂)²+(I ₁ −I ₃)²+(I ₂ −I ₃)²)}{square root over ((I ₁ −I₂)²+(I ₁ −I ₃)²+(I ₂ −I ₃)²)}  (2)

If n=3, then for a central wavelength of λ=750 nm, the small steps are250 nm each.

If camera does not have an electrical input for controlling the shutter,nor it outputs any electrical signal when the shutter button is pressed,then a 2^(nd) procedure is used, as described immediately below. Severalgroups of n images are acquired for each manual press on the shutterbutton, 9, using impulses created by photodetector 26. If this willcontinue for any press of the shutter button 9, then a too densecollection of images would be obtained. Therefore, a counter, whichafter every set of n pulses, advances the OPD by a selected value, D.This could be implemented with an extra block, a counter 118, whichclocks up to n=3, 4 or 5, depending on how many steps are collected forphase shifting interferometry, where the counter block 118 itselfchanges the OPD by a larger value D, after a number of steps n.Alternatively, the counter block 118 communicates with the PC via line119, and an input-output board in the PC 50 works out based on aprogram, the amplitude of the electrical signal to be sent to the OPDblock 110 to modify the OPD by a D step.

The user has the possibility to choose the values D of steps between theimages in the stack, as well as the current value of OPD, as shown byknobs 120 and 121 respectively. They could act either on the PC 50,which then controls the stage 115 via line 117 and vibrator 114 andphase modulator 111 via line 125. Knobs 120 and 121 could also controlblock 110 directly.

Alternatively, the function of the counter 118 can be taken by the PC,50, line 27 itself can be sent directly to the PC to work out smallsteps to be applied via line 125 and big steps D via line 117.

According to the procedure and embodiment described above, such OCTimages can be produced at low cost. Cameras of 5 Mpixels are nowcommercially available for less than 200 pound. Their flash can standover 10000 events. Several photographic flash optical sources and flashsources incorporated into digital camera box can flash a quick sequenceof three flashes or more in 1 s and collect 3 images or more insynchronism. This could ideally be used with the adapter as describedabove to produce an enlace OCT image using phase shifting interferometryprinciple with n=3 steps (or with n=2 steps applying Hilberttransformation). In this case, line 27 can act upon block 110 to producethe small steps of subwavelength values λ/n and after each press of theshutter button 9, the stage 115 is advanced manually or via the PCcontrol 50.

If the camera does not have the capability of rapid fire of sequentialflashes, then the shutter 9 has to be pressed manually for n=2 or 3times at least to acquire interference images which are later processedto produce a single OCT en-face image from a given depth.

2.3. Phase Shifting Using the Colour Sensor Parts in the Camera

In a different embodiment, the three steps required for phase shiftinginterferometry are produced using a different OPD adjusting block, 110,and employing the three colour channels in any colour CCD camera, asshown in FIG. 3. The OPD adjustment block 110 has three optical pathsseparated by dichroic filters. Let us suppose that the optical spectrumof the flash source 4 can be divided into three windows, r, g, b, wherer means the longest wavelength window, g an intermediate window and bthe shortest wavelength window. They could be associated to the threefundamental colors of the spectrum, red, green and blue. For instance,the three windows could be described by: r=570-900 nm, g=500-570 nm andb=450-500 nm. The splitter 112 b is a cold mirror which reflects thewindow b and transmit the other two band windows, the splitter 112 g isa cold mirror which reflects band g and transmits band r and 112 r couldbe a simple mirror. It should be obvious for those skilled in the artthat the same function can be equally implemented with hot mirrors, inwhich case the first reflected beam is in the r band and for the lastband, of shortest wavelength, the filter is a simple mirror. Thespectral selection is obtained in FIG. 3 in reflection. For thoseskilled in the art, it should be obvious that hot mirrors and coldmirrors could equally be used in transmission and selection of suitablecold and hot mirrors can also be practised.

Two Possible Adjustments of Phase Shifts are Possible as Described in2.3.1 and 2.3.2: 2.3.1. A Different Phase Shift Per Each Spectral Window

Waves within each spectral window r, g, b travel along independentlyadjustable path lengths using mirrors 113 r, 113 g, 113 b respectively.Their optical paths are adjusted in such a way, that for λ_(R) the OPDis zero, for λ_(G) the OPD is λ_(G)/3 and for λ_(B) the OPD=2 λ_(B)/3.It should be obvious for those skilled in the art that othercombinations are equally feasible, where the OPD is zero for λ_(G), theOPD is −λ_(R)/3 and for λ_(B) the OPD=λ_(B)/3. Each spectral windowchannel in the camera will be sensitive to the respective color returnedin the object arm from the object, 100, interfering with the similarcolor returned from the respective reference path. In this way, threeinterference frames are provided on the three colors. For each pixel inthe CCD camera, three signals are collected for the three colours. Theseare used to produce the demodulated en-face OCT image. For each pixel inthe photodetector array, let us denote I_(r), I_(g), and I_(b), theintensity of the photodetected signal provided by each colour part ofthat pixel. The following quantity is evaluated as:

s=√{square root over ((I _(r) −I _(g))²+(I _(g) −I _(b))²+(I _(r) −I_(b))²)}{square root over ((I _(r) −I _(g))²+(I _(g) −I _(b))²+(I _(r)−I _(b))²)}{square root over ((I _(r) −I _(g))²+(I _(g) −I _(b))²+(I_(r) −I _(b))²)}  (3)

If the point in the depth is outside coherence, all values are the sameand the result is zero. If interference takes place, then the quantityin (3) approximates the amplitude of the interference signal.

Alternatively, more than 3 spectral windows and steps for phase shiftinginterferometry can be implemented. For instance for 5 steps, the block110 in FIG. 3 is equipped with two more filters to separate signals in aband between b and g and a band between g and r. For these extra twosignals, a photodetected signal I_(bg) is constructed by compounding thetwo intensities I_(b) and I_(g), respectively, a photodetected signalI_(g), is constructed by compounding the two intensities I_(g) andI_(r). Equation (3) becomes:

$\begin{matrix}{s = \sqrt{\left( {I_{r} - I_{rg}} \right)^{2} + \left( {I_{rg} - I_{g}} \right)^{2} + \left( {I_{g} - I_{gb}} \right)^{2} + \left( {I_{gb} - I_{b}} \right)^{2} + \left( {I_{b} - I_{r}} \right)^{2}}} & \left( {3a} \right)\end{matrix}$

All the intensities, I_(p) with p=r, g, b, gb, rg above are normalisedsuch that for a mirror as object and when the OPD is outside coherence,all I_(p) are equal.

Three Dimensional Imaging

C-scan OCT images can be collected at different depths by repeating theprocess above for a different OPD adjusted by actuating on the stage 115or on the spectral scanning delay line in the block 110 to adjust theOPD in steps larger than the coherence length associated to theindividual spectral bands. The repetition can be actuated manually bypressing the shutter button 9 or if the camera is equipped with therapid fire feature, can be performed automatically up to the maximumnumber of flashes allowed by the flash source 4. If f=10, then 10×3interference images are collected, from each set of three images aC-scan OCT image is generated. By using Hilbert transformation, twosteps are enough and therefore the number of images required becomes10×2. In case the camera does not output pulses for each flash, then thedata acquisition can proceed using the photodetector 26 (in FIG. 2) andcounter 118. In case the colour camera has m colour sensors and theflash can burst f times in sequence, then a number of mf interferenceimages are collected and from each set of m images a C-scan image isproduced at each depth.

2.3.2. Practising the Same Step of Phase Shift in all Colour Bands

In this case, each mirror 113 r, 113 g and 113 b in the block 110 isactuated with a respective piezo 114 r, 114 g and 114 b to implementexact steps for the corresponding central wavelengths, λ_(r), λ_(g) andλ_(b). The stepping at exact values of zero in all three bands, then atλ_(r)/3, λ_(g)/3 and λ_(b)/3 and next for 2λ_(r)/3, 2λ_(g)/3 and2λ_(b)/3 is provided via control lines 126 r, 126 g and 126 brespectively.

Extending the Depth Range or Increasing the Speed of Operation

Another function of the embodiment in FIG. 2 equipped with the block 110in FIG. 3 is for covering an extended range of depths in less time. Letus consider that the target has similar spectral properties, forinstance in profilometry of a corrugated surface extending in heightvariations over R=300 microns. In that case, each colour of the sensorand the associated emitted spectrum from the optical source, 4 or 6 canbe used to cover ⅓ of the range R, i.e. R/3=100 microns. If thecoherence length of the associated spectral window bands has a similarvalue of 1_(c)=20 microns, then M=R/(31_(c))=5 steps. Using a D=20micron differential step applied via block 110 will collect for eachspectral window sufficient data to cover R/3=100 micron, and in factimages from a whole depth of 300 microns is collected. Initially, themirrors 113 r, 113 g and 113 b are adjusted for the OCT in green tostart at an OPD longer (or shorter) than that of the OCT in blue byR/3=100 microns and for the OCT in red to start at an OPD longer (orshorter) than that of the OCT in blue by 2R/3=200 microns. In 5 steps,15 C-scan images are acquired when using the rapid fire procedure of 3flashes. Three phase steps are imprinted as explained above to acquire 3interference images which are subsequently used to construct a C-scanOCT image. To perform this function, the three spectral lengths of theblock 110 have to be stepped with corresponding sub-wavelength values 0,λ/3 and 2λ/3 for each respective band.

Evaluating the Curvature of Curved Objects

If the object is a sphere and profilometry is required, or the object100 is the cornea of an eye and the curvature is required, the procedureexplained above to increase the depth range is applicable to produceprofilometry or curvature measurement. Let us say that the three colourchannel OCT systems are set via the length of the three reference pathsr, g and b in the embodiment in FIG. 3 to OPD, OPD+d and OPD+2d, where dis comparable with the coherence length, considered approximately thesame for all three spectral bands r, g, and b. Then three C-scan imagesat three different depths will be obtained, corresponding to the threevalues of OPD. If we are to consider the contour of the cornea imageonly in the C-scan image, representing the discontinuity in the index ofrefraction between air and the cornea tissue, then three circularcontours of ascending size will be obtained as the depth increases fromone channel to the other. Knowing the value d, the curvature of thecornea as well as the distance of the cornea apex from the OCT systemcould be inferred by simple Mathematics knowing the d value, asdescribed in US Patent Application, 20080170204, Method and apparatusfor determining the shape, distance and orientation of an object, withthe difference that the colour sensitive parts are used for each delay.To obtain each OCT image in each of the spectral band, three phase stepsare imprinted as explained above to acquire 3 interference images. Toperform this function, the three spectral lengths of the block 3 have tobe stepped with corresponding sub-wavelength values 0, λ/3 and 2λ/3 foreach respective band.

Speckle Reduction

A microscope slide 123 can be inserted halfway into the object beambefore the final lens 41 as shown in dashed line in FIG. 2, of such athickness as to determine an optical delay larger than the thickness ofthe object to be measured. Let us say that the object is a superpositionof layers of paint and exhibits a thickness R=0.7 mm. In this case, thedelay introduced by the plate 123 is adjusted to be d=1 mm in relationto the one way rays going through the other side of the beam nonintercepted by the plate. The OPD in the three channels, r, g, and b inthe reference paths in FIG. 3 are adjusted 1 mm apart. For instance, ther channel is adjusted to have a reference path length longer by 1 mmthan the green channel and the b channel to be shorter by 1 mm than thereference length of the g channel.

Three C-scans are obtained, one for each colour. One colour is used tocollect light which encounters the plate delay once, delay d (rays whichgo through air and in the way back encounters the plate 123, or rayswhich go through the plate and in the returning path skip the plate), inwhich case the corresponding colour reference path is adjusted to d. Thesecond colour is adjusted to match the rays which do not intercept theslide 123 at all, in which case the corresponding colour reference pathis adjusted on zero, and the third colour channel is adjusted to matchthe rays which go through the slide 123 twice (towards and backwardsfrom the object 100), in which case the corresponding colour referencepath is adjusted to 2d. The three C-scans originate from the same depthbut are produced at three different incidence angle of the incoming raysand when they are superposed in the PC, speckle will be reduced. Thebasic idea is that rays in the three channels enter the object underdifferent angles and by angular average, speckle is reduced. Here, theangular incidence of the ray on the object is encoded on wavelength.

Three phase steps are imprinted as explained above to acquire 3interference images. To perform this function, the three spectrallengths of the block 3 have to be stepped with correspondingsub-wavelength values 0, λ/3 and 2λ/3 for each respective band.

Spectroscopic En-Face OCT

Another function of the embodiment in FIG. 2 equipped with the block inFIG. 3 is that of providing spectroscopic en-face OCT. This function isuseful when the object exhibits different properties (index ofrefraction, reflectivity, scattering or absorption, polarization, etc.)variable versus wavelength. Such a case is that of measuring theconcentration of macular pigments in the eye or for oximetry of the eyeand skin. For such an operation, each colour sensor and the associatedband emitted by the optical source are used to provide OCT informationabout the object in that band. This means that at least two or threephase steps are required before a group of two or three differentspectral band C-scans are created. At each step, two or three phasesteps are imprinted as explained above to acquire 3 interference images.To perform this function, the three spectral lengths of the block 110have to be stepped with corresponding sub-wavelength values 0, λ/3 and2λ/3 for each respective band, where the OPD in the three spectral bandsselected by block 110 are substantially the same.

In the process of adjustment, a few shots are collected checking theadjustment of the depth. Using the knob 121, or manually adjusting theposition of the stage 115 or acting on the stage 115 via PC control 117,the depth where the acquisition will start for 3D imaging is adjusted.Then, a number of 3P acquisitions steps are performed under the controlof the PC. For phase shifting interferometry, as explained before, twoprocedures can be implemented. In case the camera does not output anyelectrical signal to sense the shot, then the photodetector 26 is usedto automatically advance phase steps in all three channels and at every3 steps to return the piezo 114 to zero (or two steps of half wavelengthwhen using Hilbert transformation), or move the stage 115 insubwavelength steps, by actuating on the PC50 via line 119 which willsend voltages to the piezo 114 r, 114 g and 114 b via the electronicinterface 5.

Polarisation Sensitive En-Face OCT

Light is linearly polarized by one of the elements 14, 15 or 19 (14′,15′ or 19′) and sent towards the object 100 via a wave plate, preferablyat 45⁰ from the axes of a quarter wave plate 122. Elements 116 r, 116 gand 116 b in the three reference paths are polarisation selectors. Letus consider the object 100 as an uniaxial birefringent crystal. In thiscase, for instance 116 r could be a half-wave plate oriented at 22.5⁰for the central wavelength of the red spectral band, while 116 g is azero degree waveplate or none is placed in the green reference channel.Linear polarised light traversing the waveplate 116 r twice will incur arotation of 90 degrees. In this case, the OCT C-scans delivered by thered and green parts of the sensor 3 represent orthogonal polarizationsignals, H and V respectively. Other combinations are equally possible.By evaluating:

$\begin{matrix}{s = {{\sqrt{H^{2} + V^{2}}\mspace{14mu} {and}\mspace{14mu} \phi} = {\tan^{- 1}\frac{H}{V}}}} & \left( {{4a},b} \right)\end{matrix}$

a polarization insensitive C-scan is obtained from the signal s and theorientation of the birefringence axis at the respective depth where theC-scan images are collected is given by the angle φ. Obviously, two orthree phase steps as explained above are required to obtain the signalsH and V.

The blue channel could be equipped with another waveplate at a differentangle adding another point on the Poincare sphere and allowing a furtherimprove in the evaluation of signals s and φ.

Here polarisation sensitive information from the object is encoded onwavelength using a colour digital camera.

Three phase steps are imprinted as explained above to acquire two orthree interference images. To perform this function, the three spectrallengths of the block 110 have to be stepped with correspondingsub-wavelength values 0, λ/2 when using two steps and Hilberttransformation and 0, λ/3 and 2λ/3 when using standard three phaseshifts procedure, for each respective band.

2.4. Sequential OCT/Confocal Imaging

To view the object only and perform imaging, a screen 44 can beintroduced into the reference beam. This could be a flipping screenmechanically or electrically controlled by PC 50 under line 45.

2.5 Further Details

In more detail, the embodiment relates to a camera adapter based opticalimaging apparatus to image an object which consists in an adapter and acommercially available digital camera, where the digital camera isequipped with at least an optical source, a photodetector array and amanual shutter button and where the said adapter makes use of theoptical source equipping the said digital camera to illuminate theobject observed as well as ensure that light from the optical sourcereflected from the object is transferred to the said digital camera viathe adapter and makes use of the photodetector array to produce depthresolved information about the topography of the object and about itsinternal structure.

The said adapter may incorporate a low coherence interferometer.

The digital camera may be equipped with a flash lamp normally used toilluminate the scene photographed by the said digital camera and itsoutput light is conditioned in its spatial distribution and beamdiameter by the said adapter using a flash source interface optics toilluminate the object.

The digital camera may be equipped with an IR beam used normally toilluminate the scene photographed for aiding automatic focus and wherethe said optical source is the output light resulting by conditioningthe IR beam in its spatial distribution and beam diameter by the saidadapter using an IR beam source interface optics to illuminate theobject.

The low coherence interferometer may contain at least one beamsplitterwhich divides the light from the said optical source into an object beamconveyed to the said object and a reference beam towards an opticaldelay block and where light from the object is returned via the adapterand the beamsplitter to interfere with light from the optical delayblock on the said photodetector array which acquires an interferenceimage for each press of the shutter button and where the optical delayblock is equipped with means to adjust the length of its path measuredroundtrip from the beamsplitter, and at each press of the shutter buttonthe optical delay path is adjusted to a new value.

The means of altering the reference path may be controlled by signaldelivered from the digital camera at each press of the shutter button.

The means of altering the reference path may change the length of thereference path by a subdivision, λ/n of the central wavelength λ of thespectrum of the said optical source and which brings the referencelength to the initial value after n such steps and where a C-scan OCTimage is evaluated by combining the n acquired interference images.

The camera adapter may be additionally equipped with a photodetectorwhich senses the presence of light from the said optical source,photodetector which drives a counter and where the means of altering thereference path is controlled by signal delivered by the saidphotodetector in small steps and by the said counter in big steps, wherethe small steps are cyclical and the big steps are cumulative, where thesmall steps cycle is 0, λ/n, 2λ/n, . . . (n−1) λ/n where λ is thecentral wavelength of the spectrum of the said optical source and wherefor each flash of the optical source, an interference image is collectedand stored, and where after n flashes the counter determines that acumulative OPD=D step is imprinted to the said delay adjustment blockbefore acquiring the next set of n interference images from a differentdepth incremented by D in the said object in comparison with theprevious depth and where a C-scan OCT image is evaluated at depthsmultiple of D for each set of consecutive n acquired interferenceimages.

The sensor array in the digital camera may be a colour array whichdelivers signals from each pixel corresponding to spectral components inthree bands, r, g, b, centred on respectively λ_(r), λ_(g), λ_(b) aspart of the spectrum of the said optical source and the optical delayblock operates spectral selection in the three separate reference paths,r, g, b equipped with three r, g, b arms tuned on the three spectraldifferent bands, the optical delay block returning three optical r, g, bwaves to the said beamsplitter and where each reference path r, g and bcan be independently adjusted in relation to the other two.

The means for adjusting the path length in the said optic delay blockmay consist in a spectral scanning delay line equipped with at least adispersing (diffraction) element, a focusing element and a tiltingmirror whose tilt can be actuated via electrical signal input.

The three spectral reference paths r, g, b may be adjusted to generatean optical path difference between each reference path length and theobject path length of 0 λ_(i), λ_(j)/3 and 2λ_(s)/3 where i, j and scould be any set of permutations of r,g,b and where three interferenceimages are generated by the said colour sensor array, one for each bandr, g, b, with I_(r), I_(g), and I_(b), the intensity of thephotodetected signal provided by each colour part of the said camerapixels and where a C-scan OCT image is assembled for each pixel usingthe values delivered by the colour parts of the same pixel in the threeinterference r, g, b images evaluated as: s=√{square root over((I_(r)−I_(g))²+(I_(g)−I_(b))²+I_(r)−I_(b))²)}{square root over((I_(r)−I_(g))²+(I_(g)−I_(b))²+I_(r)−I_(b))²)}, where such OCT image isgenerated after pressing the said shutter button once.

The three spectral reference paths r, g, b may be adjusted to generate:at the first press of the said shutter button, an optical pathdifference between each reference path length and the object path lengthof zero, the adapter collecting intensities I_(1p), with p=r,g,b,

at the second press of the shutter button, OPD values of λ_(r)/3 in ther reference path, λ_(g)/3 in the g reference path and of λ_(b)/3 in theb reference path, the adapter collecting intensities I_(2p), withp=r,g,b,and at the third press of the shutter button, OPD values of 2λ_(r)/3 inthe r reference path, 2λ_(g)/3 in the g reference path and of 2λ_(b)/3in the b reference path, the adapter collecting intensities I_(3p), withp=r,g,b and where three C-scan OCT images of s_(p)=√{square root over((I_(1p)−I_(2p))²+(I_(1p)−I_(3p))²+(I_(2p)−I_(3p))²)}{square root over((I_(1p)−I_(2p))²+(I_(1p)−I_(3p))²+(I_(2p)−I_(3p))²)}{square root over((I_(1p)−I_(2p))²+(I_(1p)−I_(3p))²+(I_(2p)−I_(3p))²)} on each pixel withp=r, g, b are assembled for each colour r, g, b of the colour parts ofthe pixels in the said photodetector sensor array from the threeinterference images acquired for the three presses of the shutterbutton.

The digital camera optical source can fire three flashes in sequencefrom the said optical source at one press of the shutter button andwhere the intensities I_(1p) are collected using the first flash,intensities I_(2p) are collected using the second flash and intensitiesI_(3p) are collected using the third flash automatically.

In order to produce a C-scan OCT image of less speckle, the adapteradditionally uses a microscope slide of thickness providing an opticaldelay d for the rays going through it in comparison with the raysthrough air, plate which is introduced halfway through into the objectbeam and the spectral reference paths r, g, b in the reference block areadjusted in steps of d

For polarisation imaging, each spectral path r, g, b in the optic delayblock is provided with a polarisation element imprinting a differentpolarisation characteristic to each reference wave returned to thebeamsplitter and where the said polarisation element is chosen from thecategory of linear polarisers or waveplates.

For curvature evaluation, the three spectral reference paths areinitially adjusted on 0, d and 2d, where d is larger than the coherencelength corresponding to the individual bands and where phase shifts areapplied to each path in the optic delay block to generate a C-scan OCTimage at 0 depth in the first band, a C-scan OCT image at d depth in thesecond band and a C-scan OCT image at 2d in the third band when thefirst, second and third band could be any of the r, g or b band and bysuperposing the three C-scan OCT images in one compound frame andmeasuring the differential distances between different contours suchcreated in the compound frame, evaluate the curvature of the objectsurface.

3. CHANNELED SPECTRUM OCT

Another embodiment of the present invention is shown in FIG. 4. Here,the adapter 10 transforms the camera into a channeled spectrum OCTsystem which can produce A-scans or OCT cross sections images (B-scanimages) from the object, 100.

The key element is an optical dispersing component 42, which could be aprism or a diffraction grating, preferably a diffraction grating intransmission for its small volume and high dispersing power.

Phase shifting interferometry is no longer required and therefore themodulator 111 and piezo 114 may not be necessary, unless complex Fouriertransform is evaluated as disclosed below.

1D OCT images, A-scans reflectivity profile are obtained along thespectral decomposition direction of the camera. Preferably, a number ofpixels larger than 512 should be set along the dispersion direction, asthis number multiplied by a quarter of the coherence length of theoptical source determines approximately the depth range. The directionof pixels perpendicular to the spectral decomposition direction haslittle use here. Advantageously however, as the aberration of the opticslead to extended diffracted spots, more than one line of pixels of the2D sensor array 3 should be collected (binned), this also results inenhanced sensitivity and increased speed. In the case of 3/2 cameraratio format, preferably the X direction (with the largest number ofpixels), or the direction with the larger number of pixels should beoriented along the spectral decomposition direction, which in FIG. 4 isin the plane of the drawing.

To convey the light from the interferometer to spectral analysis via thedispersing element 42, a spatial filter 61, a converging element 62 andanother spatial filter 63 may be used. To convey the dispersed lightfrom the dispersing element 42, through the camera lens 21, asupplementary converging element 64 may be required. In case thefocusing element 21 is detachable, other converging elementsconfiguration may be used according to means known in the art. In orderto generate a linear distribution of the output sensor 3 versuswave-numbers, a supplementary dispersing element, 65 may be used, asdescribed in the paper “Fourier domain optical coherence tomography witha linear-in-wave number spectrometer”, by Chilin Hul, and Andrew M.Rollins, published in Optics Letters, Vol. 32, No. 24, 2007, pp.3525-3527, otherwise the linearization in wave-numbers is produced bysoftware means in the PC 50 after download of the images from theinterface 5.

Converging elements above could be any lenses or curved mirror.Dispersing element 65 could be a prism or a diffraction grating,

Focusing elements 11 and 11′ include schematically the spatialfiltration provided by two focusing elements 11 a, 11 b and the pinhole18, respectively the elements 11 a′, 11 b′ and 18′ as detailed in FIGS.1 and 2 but now shown here.

Typical applications are measurement of the thickness of thin objects,such as cornea, paper, object of arts, the depth of scratches ofinterest in forensic analysis, etc. The optical path length of theanterior chamber of the human eye or of the whole eye if measured canprovide important information on the health state of the human. It isknown that the sugar content in the blood is also reflected in the eye.Therefore, by measuring optical path lengths in the eye, the content ofsugar or of other constituents can be estimated. The optical path lengthis the product of the geometrical path by the index of refraction, andthis is what is altered by chemical constituents, such as sugar. Assugar is also optically active, polarisation measurements can be addedfor enhanced accuracy by using different colour parts of the sensor asdescribed above using reference paths customised for differentpolarisation states. Such a system using the adapter and a camera canreplace the invasive method used today by diabetics who regularly pricktheir fingers.

Tear film thickness can be evaluated as well as information on dry eyescan be obtained using OCT A-scans.

As several cameras are now commercially available which are water proof,a compact system can be assembled to perform under water imaging, forinstance to investigate the integrity of translucent machinerycomponents or art objects. Black and white as well as colour cameras canbe adapted, in which case a grey scale is obtained by known means ofsumming or weighting the contributions of the three spectral sensingparts.

3.1. Complex Channeled Spectrum OCT

Although phase shifting interferometry used by the embodiment in FIG. 2is no longer necessary for CS-OCT, it could still be conveniently usedfor elimination of mirror terms. If OPD=0 is placed inside the object100, mirror terms will distort the image, due to the fact that the samechanneled spectrum results for positive and negative OPD values of thesame modulus value. The same principle of phase shifting interferometry,with three subwavelength small displacements could be employed toeliminate the mirror terms. Different solutions are possible, such asusing at least three subwavelength shifts employing the piezo ormagneto-strictive element 114, or using a frequency shifter as describedin the “Heterodyne Fourier domain optical coherence tomography for fullrange probing with high axial resolution”, by A. H. Bachmann, R. A.Leitgeb, T, Lasser, published in 14(4), Opt. Express (2006) 1487-1496.Three phase shifts can advantageously be introduced using the embodimentof the block 110 in FIG. 3 which can replace the simplified block 110shown in FIG. 4 for those objects which do not present spectraldependence of reflectivity nor spectral dependence of any otherparameters involved in signal generation. In this case, the threechannels, r, g, b can simultaneously provide interference signals whichcan conveniently be combined to eliminate the signal at zero frequencyas well as the mirror term. Three A-scans are acquired using the r,g,bcomponents of the RAW image provided by the camera. In principle, usingthree phase steps is sufficient to assemble complex Fourier transformand double the depth range of CS-OCT.

Similarly, using a frequency shifter as the optical modulator 111, thechanneled spectrum is modulated with the signal applied to 111. Forinstance, reading the camera twice during a period of the signal appliedto 111, delivers a cycle of modulation of the channeled spectrum. Signalapplied to 111 can be sinusoidal of frequency 1 kHz and camera read in0.5 ms. This can be achieved by collecting two shots at 0.5 ms apart.Some specialised camera can acquire two images during a single flashburst. In this case, the sequence of data trigger can be applied to 111,to apply max voltage for the first data acquisition step and applyingzero voltage or minus voltage during the second data acquisition step.The flash duration is adjusted to last sufficiently long to allow thisprocedure. In the same way, by applying subdivisions of the voltage to111 in synchronism with data acquisition steps, more than two images canbe collected per modulation cycle. The images so collected aresubsequently used to provide full range FDOCT B-scan images withelimination of mirror terms. This procedure can conveniently be combinedwith that using the three colours in the sensor 3, which together withdifferent waveplates (phase shifts) can provide more points andrespectively as many images which subsequently could be manipulated toproduce a better full range B-scan image.

Polarisation Sensitive A-Scanning

Light is linearly polarized by the polariser 14 and rotated by thehalf-wave plate 15 for the flash source and polariser 14′ and rotated bythe half-wave plate 15′ for the IR beam and sent towards the object 100via a quarter wave-plate 122, preferably at 45⁰ from its axes to launchcircular polarised light towards the object. The three OPD values forthe three path length of the spectral bands r, g, b are adjustedessentially the same using the mirrors 113 r, 113 g and 113 b in theembodiment of the block 110 in FIG. 3 which can be incorporated into theembodiment in FIG. 4. Elements 116 r, 116 g and 116 b in the threereference paths are polarisation selectors. Let us consider the object100 as a uniaxial birefringent crystal. In this case, for instance 116 rcould be a half-wave plate oriented at 22.5⁰ for the central wavelengthof the red spectral band, while 116 g is a zero degree waveplate or noneis placed in the green reference channel in which case the OCT A-scansdelivered by the red and green parts of the sensor 3 representorthogonal polarization signals, H and V respectively. Othercombinations are equally possible. By evaluating:

$\begin{matrix}{s = {{\sqrt{H^{2} + V^{2}}\mspace{14mu} {and}\mspace{14mu} \phi} = {\tan^{- 1}\frac{H}{V}}}} & \left( {{5a},b} \right)\end{matrix}$

a polarization insensitive A-scan is obtained from the signal s and theorientation of the birefringence axis along the depth is given by theangle φ.

The blue channel could be equipped with another waveplate at a differentangle adding another point on the Poincare sphere of the object andallowing a further improve in the evaluation of signals s and φ versusdepth. It should be obvious for those skilled in the art that othercombinations of plates 15 (15′), 122 and 116 r, 116 g and 116 b arepossible to obtain three or more polarisation data values.

Speckle Reduction

A microscope slide 123 as shown by the dashed line in FIG. 4 can beinserted half-way through into the object beam before the final lens 41of such a thickness as to determine an optical delay larger than thethickness of the object to be measured. Let us say that the object is asuperposition of layers of paint and exhibits a thickness R=0.7 mm. Inthis case, the delay introduced by the plate 123 is adjusted to be 1 mmfor the rays going through in comparison to the rays going through theother side of the beam which are not intercepted by the plate. The OPDin the three channels, r, g, and b in the reference paths in FIG. 3 ofthe block 110 which can be incorporated in FIG. 4 are adjusted 1 mmapart. For instance, the r channel is adjusted to have a reference pathlength longer by 1 mm than the green channel and the b channel to beshorter by 1 mm than the reference length of the g channel.

Three A-scans are obtained of the depth R distributed over the wholeline of pixels, according to wavelength. They are then superposed in thePC reducing the speckle, according to the procedure described by N.Iftimia, B. E. Bouma, and G. J. Tearney, in Speckle reduction in opticalcoherence tomography by “path length encoded” angular compounding, J.Biomedical optics, 8(2), 260-263 (2003). The basic idea is that rays inthe three channels enter the object under different angles and byangular average, speckle is reduced, similar to the procedure describedat point 2 above using a C-scans.

Spectroscopic A-Scanning

In case the object has spectral properties, such as tissue, then it isimportant to provide spectroscopic OCT data. It is known that bymeasuring the reflectivity at different wavelength values, spectralabsorption or spectral scattering can be assessed. Oximetry is one suchfield which can benefit. For oximetry for instance, the optical filter19 has three peaks optimised on wavelengths to maximise the accuracy ofoxygen concentration when using the three images delivered by the threecolour parts of the sensor 3.

Black and white as well as colour cameras can be adapted, in which casea gray scale is obtained by known means of summing or weighting thecontributions of the three spectral sensing parts.

Channeled Spectrum B-Scan Imaging

Two possible avenues of improving the embodiment in FIG. 4 are disclosedto produce B-scan OCT images.

Using a Transversal Scanner

A transversal scanner 85 can be added to scan the object beam over thetarget, using one or two mirrors, by means known in the art, such asgalvo-scanners, resonant scanners, acousto-optic modulator or any othermeans which can scan the object beam angularly or laterally.Alternatively, a sliding mechanism, 91, can be used to laterally movethe whole adapter and digital camera for manual scanning. For eachlateral position achieved by actuating on the transversal scanner 84 orsliding mechanism 91, another A-scan is produced. By collecting severalsuch A-scans for several presses of the shutter 9, and in this way aB-scan image can be assembled putting together the A-scans.

Light Line

Instead of projecting a spot to collect an A-scan from the depth at thespot location, a light line could be projected on the target and withcylindrical optics, better use of a 2D photosensor array is achieved, aspresented by Endo, T., Yasuno, Y., Makita, S., Itoh, M. and Yatagai, T.,in “Profilometry with line-field Fourier-domain interferometry,”published in Opt. Express 13, 695-701 (2005). An additional cylindricallens 66 is used to project a line illuminating image from either of thetwo sources, 4 or 6, on the sample 100, or this could be accomplished byconverging optics 11 or 11′ (which contains a spatial filter as well,18, as detailed in FIGS. 1 and 2). In FIG. 4, the cylindrical lens 66creates an illuminating line perpendicular to the figure plane. Some ofthe camera flashes are equipped with linear flash sources, in the formof linear filament bulbs or line capillaries filled with gas, othershave their flash made from segments, in which case a linear segment canbe advantageously used to generate a line. In this case, the cylindricallens to condition the beam shape to a line is not necessary and aspatial filter 18 may be sufficient to spatially filter the flash light,in the form of a line slit. The light scattered back from the object 100is transferred to the diffraction grating 42 where it is diffracted overthe horizontal line of pixels in the photodetector array 3. If thecamera has N lines and M columns of pixels, then for each pixel, (X,j)in the line projected on the object 100, for j=1 . . . N, a spectrum isdispersed over the (1,j) to (M,j) pixels in the photodetector arrayline, j. The length of the line projected on the object 100 is returnedto the columns of the photodetector array via lenses 41, 13, 62, 64 and21 in the interface optics covering all columns, each column up to Mmeaning also three colour columns.

In the reference path in the block 110, another cylindrical lens isadded, 67. The spatial filter 61 is a vertical slit in this case.

When using line illumination, the transversal scanner 85 has one mirroronly to provide the repetition of B-scans for a different angulardeflection of the beam. For each position, a new flash is shot and a newB-scan is acquired. For faster acquisition, the camera flash is replacedwith an external faster flash unit. Alternatively, the IR beam emittedby 6 is continuously used. For even faster acquisition, an external morepowerful optical source may be used in conjunction with the camera, 4″.

Before any image acquisition, a screen 43 is introduced in the objectbeam to acquire images without the object. The images collected with thescreen in, are deducted from images collected with the screen 43removed. This eliminates or at least reduces the autocorrelation termsdue to the reference beam.

Several images can be acquired in one flash burst, of the source 4 or 4″as well. In this case the flash is made longer and the camera isswitched into movie regime.

Balance Detection Using Two Cameras

Another embodiment of the present invention is presented in FIG. 5. Heretwo cameras, 1 and 1′ are used, secured to the adapter in place viasupports 90 and 90′ and the reference beam transmitted via mirrors 112and 132 on the stage 115, towards a second optical splitter, 75. Splitreference beams 32, 32′ and object beams 31 and 31′ are sent to twoconventional commercially available cameras 1 and V. The amount ofoverlap of object and reference beams on the gratings 42 and 42′ isadjusted via a displacing means equipped with mirror 132 using a stage135 and splitter 75. The signals from the two photodetector arrays, 3and 3′, are deducted and in this way, the noise around 0 Hz component islargely reduced, along with autocorrelation components within thereference beam and object beam. Two possibilities exist, either the twosignals delivered by the photodetector arrays are subtracted, in casethey are analogous and then the signal is digitized and an image iscreated by the PC 50. Simpler, the two images from the memory cards, 51and 51′, or the two digital images are directly fed via lines orremotely via 55 and 55′ into the PC 50 and subtracted pixel by pixel.This is simpler but has the disadvantage of needing high dynamic rangedigital cameras. Both cameras are switched simultaneously using amechanical device 56. Alternatively, if the cameras admit remotecontrol, or external shutter facility, this will be used under a triggercontrol delivered by the PC 50.

In addition, light from both camera sources could be used to enhance thesignal to noise ratio. Addition of IR beams from both sources 6 and 6′is shown in FIG. 5, although addition could be implemented for the flashbeams emitted by sources, 4, as well.

The problem of mirror terms mentioned before in connection with theembodiment in FIG. 4 could here be addressed by altering the overlap ofreference beams, 32 and 32′ and object beams, 31 and 31′, beforereaching the diffraction grating 42 and 42′, according to principlesinspired from the theory pf Talbot bands as disclosed in the applicationWO2005040718 (A1) (GB2407155 (A) or EP1687586 (A0).

To adjust the OPD and compensate for dispersion, a method of spectralscanning delay line could be used as disclosed in WO2006024152 (A1).

Black and white as well as colour cameras can be adapted, in which casea gray scale is obtained by known means of summing or weighting thecontributions of the three spectral sensing parts.

Simultaneous Reading of all Spectral Bands by the Same Set of Pixels

In previous embodiments, the colours from the smallest wavelength in theband b to the largest wavelength in the band r are dispersed along thesensor chip. In the example on using the camera for speckle reduction,if each A-scan covers 2 k pixels, then a 6 k line of pixels sensor isrequired. Each pixel however, outputs three signals depending on itscolour filter. For the three groups of 2 k pixels, only one colour isused while the other two signals are discarded. Depending on theposition of the pixel along the line of pixels within the dispersedline, the colour channel used and the two colour channels which areunused change. This is a waste of signal and time which can be improvedusing the embodiment in FIG. 6 where a multiplexer 140 superposes allthe three bands on the same pixels. In this case, three A-scans can becollected with the same number of 2000 pixels in the example above, withadvantage of speed and cost in the size of the sensor.

It is therefore advantageous to superpose the three bands along the sameset of pixels in the camera. Let us say that for a given incidencedirection to the diffraction grating, the diffracted angles of the raysin the centre of the three bands are φ_(r), φ_(g), and φ_(b). If theincident beams are adjusted with incidence varying according to theseangles, then all three bands will be approximately superposed whendiffracted within the same order of diffraction by the diffractiongrating in reflection, 42 in FIG. 6. It should be obvious for thoseskilled in the art that equally, the diffraction grating can be used intransmission as well. To achieve the multiplexing, light out of thesplitter 25 is diverted via mirror 141, towards the diffraction grating42 after being reflected by a dichroic mirror, 142 which reflects oneband and transmits the other two bands towards mirror 143, wherefromlight is directed towards dichroic mirror 144 which reflects a secondband towards the grating 42 and the mirror 145 sends the third bandtowards the grating 42. By adjusting the distance between dichroicmirror 142 and mirror 141 and between dichroic mirror 144 and mirror145, the incidence angles on the grating are conveniently adjusted insuch a way, as all bands around a λ_(r), λ_(g), λ_(b) are diffractedalong a similar direction. A focusing element, a lens or a curved mirror64 is used to convey the spread spectrum through the camera objective21. Alternatively, if objective 2 could be removed, the focusing element64 alone spreads the spectrum along the spectral direction over cameralines and the adapter is supplementary equipped with a covering lid, 150to prevent any other light falling on the sensor 3. For instance, let ussay that the optical source spectrum is 250 nm and three bands of 50 nmwidth each are spectrally selected about three peaks λ_(r), λ_(g),λ_(b)=675 nm, 575 nm and 475 nm, with three spectral gaps for betterrejection of the other colours by each pixel, i.e. for lower cross-talk.It may be that each camera exhibits a different wavelength peak for thespectral windows r, g and b, the values above are for example only. Darkseparating bands are also useful, because inside these spectral gaps,the transition of dichroic mirrors (filters) could be safely placedwithout distorting the associated correlation function on each channelwhich determines the depth selection. These dichroic mirrors are 112 band 112 g in the reference arm and 142 and 144 in the object arm. Forthis example, the dichroic mirror 142 could be a hot mirror withtransition at 625 nm, while dichroic 144 is a hot mirror with transitionat 525 nm. In this way, mirror 141 reflects the r peak of the spectrumwith a maximum at 675 nm and the mirror 145 reflects the b peak of thespectrum with a peak at 475 nm.

The numerical values are for illustration only, the person skilled inthe art should be able to adjust the filters correspondingly to fit anycamera specs.

The multiplexer 140 could equally be used in the embodiment in FIG. 4equipped with cylindrical optics to project a line over the object to beimaged. Equally, the multiplexer 140 can be used in a balance detectionconfiguration of two cameras as disclosed in FIGS. 5 and 8. Possibly,two such multiplexers can also be employed, one for each diffractiongrating 42, 42′ and each camera, 1 and 1′.

Enhancing the Accuracy of Spectroscopic Channeled Spectrum OCT

The three paths in the reference arms in the embodiment in FIG. 6 areadjusted to be substantially equal. Three A-scans (or B-scans ifcylindrical optics is used and a line is projected on the object) areproduced by using the three spectral sensing parts r, g and bsimultaneously. In this case, the narrow band filter 19 in front of theflash source 4 can be changed and acquisition repeated. For instance, 19could be a filter with three narrow peaks, a peak in each of the band,r, g and b. Similar filters could be used in the r, g and b paths inFIG. 3. In one step acquisition, three A-scans are acquired for the setof filters. Then the filters are changed, where 19 has again threepeaks, with a peak in each of the r, g and b bands but different fromthe previous case. For instance a long three peaks and a short threepeaks filter 19 could be used, with the long filter with three peaks inthe longer parts of the r, g and b bands while the short filter withthree peaks in the shorter wavelength parts of the r, g and b bands. Inthis way, 6 A-scans can be acquired in two shots, 3 A-scans per eachfilter.

Another alternative is for filter 19 and filters 124 r, 124 g, 124 b tobe changed electrically under the line control 127 r, 127 g, 127 brespectively. Liquid crystal filters are known which can electrically betuned. In this way, spectroscopic depth analysis can be performed bycollecting 6 A-scans for 6 different wavelengths in two shots only.

Simultaneous Acquisition of Microscopy Like and Cross Section OCT Images

An embodiment for simultaneous imaging in two channels is disclosed inFIG. 7. Here the translation stage 115 is used to shift the referencebeam, 32, by reflection on the beamsplitter 75, just sufficientlylaterally from the transmitted object beam, 31, in order to ensure thatthe aperture of the confocal receiver 261 intercepts the object beamonly. In this embodiment, for reduced losses, the beamsplitter 75 has alow reflectivity and high transmission. To restrict the aperture of theconfocal receiver 261, optical fibre, a pinhole or a slit in front ofthe receiver 261 can be used, this also enhance the confocality. In theembodiments in FIGS. 4-6, simultaneous imaging in two channels is notpossible as the object and reference beams are superposed. Sequentialimaging in these embodiments becomes possible by blocking the referencebeam. However, it is important to have an en-face image to guide theinvestigation in the OCT regime. This would require diverting some ofthe object beam towards a photodetector or a different camera. Thiswould reduce the intensity of interference. Therefore, the embodiment inFIG. 7 makes use of the zero order of diffraction which is not used inthe CS-OCT regime and is discarded in the embodiments in FIGS. 4-6.Alternatively, when the dispersing element in the spectrometer is usinga prism instead of the diffraction grating 42, the embodiment makes useof the light reflected from one of the prism facet. To use this signal,first the reference beam is shifted laterally. It is now obvious thatthe reason for the lateral relative shift of the two beams in theembodiment in FIG. 5 is different than that in FIG. 7. In FIG. 5, thegoal was to eliminate the mirror terms. In FIG. 7, the goal is to shiftthe beams laterally just sufficient to eliminate the reference beam fromthe aperture of the confocal receiver 261. In the embodiment in FIG. 7,mirror terms will still exist, but reduced proportional to the amount oflateral shift of the two beams, object and reference.

The signal from the confocal receiver 261 is applied along line 262 tothe measuring block, 52, in the PC 50. In case a galvoscanner is added,85, the measuring block 52 operates as a frame grabber to generate thefundus or SLO image or microscopy image. The galvoscanner is controlledby block 53 in the PC50.

Two Regimes of Operation are Possible

Flying Spot

In this case, the output beam is focused to a point in the object. Theadapter with the camera is used for simultaneous measurements ofintensity provided by the receiver 261 and a reflectivity profile indepth, A-scan is generated using the sensor 3, read as a line camera.

For imaging, an XY-scanner head 85 is added which is equipped with twomirrors and the beam is scanned in a raster fashion using the driver 84.The confocal receiver 261 is in this case a point photodetector.Simultaneous OCT volume acquisition using the sensor 3 and en-face SLO(microscopy) imaging using photodetector 261 is achieved by using thetransverse scanner 85. Here the sensor 3 is used to generate A-scans andthe volume is assembled from such A-scans or from B-scans formed bygrouping several A-scans.

Flying Line

In this case, a line is generated using cylindrical optics to projectthe source beam in the shape of a line on the object, or by using a lineshaped optical source, such as a line filament bulb or a discharge gassource with the gas confined to a cylindrical shape. Simultaneousmeasurement is possible where the line camera 261 provides an integratedT-scan from the object over the depths within the confocal profile andthe sensor 3 provides a B-scan OCT image. Conventional 2D camerascustomised as line cameras can be used as well as linear CCD or CMOScameras, analog or digital. To restrict the aperture of the confocalreceiver, a slit can be used in front of the line camera 261. For volumeimaging, a scanner head 85 is added which has one galvo-mirror only andthe driver unit 84 requires one generator only. The sensor 3 is used todeliver a B-scan OCT image for each position of the galvomirror 85.

Simultaneous OCT volume acquisition using the sensor 3 and en-face SLO(microscopy) imaging using the line camera 261 is achieved by using thetransverse scanner 85. Here the sensor 3 is used to generate B-scans andthe volume is assembled from such B-scans while the T-scans generated bythe line camera 261 are grouped together within an en-face image(microscopy, SLO or fundus image).

Let us say that the camera 1 operates at 100 microsecond acquisitiontime. Then, a flash source emitting for slightly longer than 10 ms or acontinuous source 4″ can be used to acquire several shots, let us say100, and in doing so, the galvo 85 moves the line projected on thesample to a new line position out of 100 possibilities within the rasterto be finally produced. The frame grabber 52 now collects line data foreach new line position and generates an en-face SLO or microscopy imagefrom 100 such T-scans. The en-face image is completed and displayed bythe frame grabber 52 in the PC 50, while the volume is acquired by theOCT channel. 100 B-scan OCT cross sections are ready for subsequentinspection. The en-face image so generated can advantageously guide theacquisition of volumes as well as its subsequent visualisation ofdifferently oriented sections in the object. This image is not inferredlike in prior art from B-scans, but generated live using signal in thezeroth order of diffraction (when using a diffraction grating) orreflected by the prism in the spectrometer set-up when using a prism.

The embodiment in FIG. 8 represents an efficient set-up, where allsignals out of the beamsplitter 75, now 50/50, are used. A balancedconfiguration with two cameras, 1 and 1′ for balanced OCT and twophotodetectors, 261 and 261′ are used to intercept the zero order ofdiffraction. Here the translation stage 115 is used to shift thereference beam just sufficiently laterally in order to ensure thatphotodetector 261 and 261′ intercept the object beams only. Pinhole 263,263′, slits or fibre optics are used to restrict the aperture of thephotodetectors 261 and 261′. The signals delivered by the two camerasare deducted in the differential amplifier 54. The signals delivered bythe two confocal receivers 261 and 261′ are summed up in the summator57.

Alternatively, for the embodiments in FIG. 4-6 where line shaped beamsare used to illuminate the object, separate line optical sources can beemployed for better performance. Such a source could be a stripe shapedSLD, a filament bulb or a linear discharge gas lamp with betterstability of the discharge than the lamps used in cameras.

The embodiment in FIG. 7 is implemented with division of light usingoptical fibre as disclosed n FIG. 9. Light from the optical source isconfined to the directional coupler 25, replacing the main bulk splitterin previous embodiments. Light is divided into two arms, object, alongthe circulator 81 and reference arm, circulator 81′. Light at the fibreoutputs is collimated using focusing elements 82 and 82′. The collimatedbeams via transmission through splitter 75 and respectively reflection,reach the diffraction grating 42. The splitter 75 has a highreflectivity and low transmission. To adjust the gap, d, between the twobeams, object 31 and shifted reference, 32, displacing means are used,equipped with the splitter 132 which can be moved using the translationstage 135 and a splitter 75 which can also be moved horizontally. Thespectrometer set-up consists in the dispersing element 42, focusingelement 21 and sensor 3. A pinhole 263 is used to obscure the zero orderof the diffracted reference beam, 32.

It should be obvious for those skilled in the art to customise the zeroorder diffraction order signal in the embodiments in FIGS. 7, 8 and 9into providing the SLO as well as a fluorescence signal, as allwavelengths are angularly diffracted along the same direction in thezero^(th) order. Suitable spectral filters could be used in conjunctionwith other confocal receivers (in the form of point photodetectors orline cameras) to provide confocal and fluorescence signalssimultaneously.

It should be also obvious that were a diffraction grating was used as adispersing element, a prism could equally be used and the other wayaround. If the dispersing element was a prism, then reflections from theprisms can be used to generate the simultaneous measuring signal in theconfocal receiver, and the prism can be supplementary coated with areflective layer to enhance this reflection. If the dispersing elementwas a diffraction grating, then the zero order of diffraction is used togenerate the confocal signal, in this case preferably the effort is inconcentrating the power towards the diffraction order used, byprocedures known by the diffraction grating manufacturers, such asblazing. Obviously, in the embodiments presented where a diffractiongrating is used in transmission, it could equally be used in reflectionand in the embodiments presented where a diffraction grating is used inreflection, could equally be used in reflection.

Further Details

The further details set out below may be provided in the adapter aloneor in combination.

The camera adapter based optical imaging apparatus may be equipped witha first dispersing element to provide spectral analysis of the lightoutput from the said interferometer along one directions of pixels inthe said photodetector sensor representing a spectral direction and byevaluating the Fourier transformation of the signal collected along thespectral direction covering the spectrum of the said optical source,producing a depth reflectivity profile of the object.

The dispersion element may be a prism.

Alternatively, the dispersion element may be a diffraction grating.

The camera adapter may be equipped additionally with a second dispersingelement separated by a focusing element from the said first dispersionelement to linearise the signal output of the photodetector sensor alongthe spectral axis versus the wave-number 2π/λ□ with λ the wavelength ofthe said optical source.

The sensor array in the digital camera may be a colour array anddelivers signals from each pixel corresponding to spectral components inthree bands, r, g, b, centred on respectively λ_(r), λ_(g), λ_(b)wavelength values as part of the spectrum of the said optical sourcewhich when downloaded from the pixel lines along the spectral axis ofthe said photodetector array produces via Fourier transformation anr-A-scan, a g-A-scan and a b-A-scan and light from the interferometer isspectrally split in angle using spectral splitters and mirrors in such away as the three optical bands, r, g, b fall at different incidenceangle on the 1^(st) dispersion element in such a way that all bands aredispersed along substantially the same direction along the saidphotodetector sensor. In order to use the same set of pixels forphotodetecting all three bands simultaneously, the optical delay blockoperates spectral selection in the three separate paths, r, g, b alongthree r, g, b arms tuned on the three spectral different bands, theoptical delay block returning three optical r, g, b waves to the saidbeamsplitter, where each wave encounters a different path lengthindependently adjusted in relation to the other two.

The three path lengths, r, g, b in the optical delay block may beadjusted to be substantially the same and the said photosensor arrayoutputs three A-scans, one for each colour r, g, b and where the threeA-scans, r-A-scan, g-A-scan and b-A-scan provide depth resolvedspectroscopic information about the object at one press of the shutterbutton.

The adapter may additionally use a microscope slide providing an opticaldelay d for the rays going through it in comparison with the raysthrough air which is introduced halfway through into the object beam andthe spectral paths r, g, b in the optical delay block are adjusted insteps of d to substantially superpose in depth the r A-scan, the gA-scan and the b A-scan to reduce the speckle within a compoundresulting A-scan at one press of the shutter button.

The flash optical interface may prepare a polarisation state for theoptical source light and the three reference paths lengths, r, g, b inthe reference block are adjusted to be substantially the same and whereeach spectral reference path r, g, b is provided with a polarisationelement imprinting a different polarisation characteristic to eachreference wave returned to the beamsplitter and where the saidpolarisation element is chosen from the category of linear polarisers orwaveplates and the said photodetector outputs three A-scans, one foreach colour r, g, b and where the three A-scans provide depth resolvedpolarisation information about the object at one press of the shutterbutton.

The optical source interface may project a line over the object usingcylindrical symmetry optics and at least one focusing element before thedigital camera has cylindrical symmetry where the image captured by thesaid photodetector array is a B-scan image formed from A-scans along thespectral decomposition axis and lateral extension along the direction ofthe line projected by the optical source interface over the object.

The focusing element with cylindrical symmetry may be a cylindricallens.

The focusing element with cylindrical symmetry may be a cylindricalmirror.

In case the camera flash has cylindrical symmetry, then linear spatialfilters are used in the optical source interface.

The low coherence interferometer contains two beamsplitters to route theobject and reference beams to implement balance detection and conveysubstantially equal strength object beams and equal strength referencebeams to two similar digital cameras and where the images from the twoimages are subtracted.

The 1^(st) beam-splitter divides the light from the said optical sourceinto an object beam conveyed to the said object and a reference beamtowards an optical delay block and where light from the object isreturned via the adapter and the 1^(st) beamsplitter to a 2^(nd)beamsplitter and where the optical delay block works in transmissionsending the reference beam towards the 2^(nd) beamsplitter and where thesecond beamsplitter has a ratio of 50/50.

Simultaneous measurements and dual channel simultaneous imaging based onspectral interferometry and confocal detection are made possible byemploying the stray signals when performing spectral decomposition. Whenspectral decomposition is achieved via diffraction using a diffractiongrating in transmission or in reflection, the stray zero diffractionorder is employed by a confocal receiver. When spectral decomposition isachieved via dispersion using a prism, then reflections from the prismfacets are used in the confocal receiver. These stray signals areproportional to the intensity of the object beam incident on thediffraction grating or on the prism used by the spectral decompositioncomponent. To avoid saturation of the confocal receiver due to thestrong signal in the reference arm, the reference beam is laterallyshifted before spectral decomposition away from the confocal aperture.

Simultaneous measurement and imaging in two channels OCT and confocal(SLO) can operate with one or two cameras in a balance detectionconfiguration for the OCT channel and by summing the two stray signalsfor the confocal detection.

4. SUMMARY OF METHODS

A method of high resolution depth resolved measurement of an objectwhich employs an adapter which transforms a commercially availabledigital camera into a depth resolved measurement instrument, by makinguse of the elements equipping the commercially available digital camerato illuminate the object observed as well as ensure that light from theobject is transferred to the said commercially available camera, andwhere the said commercially available camera is equipped with at leastan optical source, a photodetector array and a shutter button.

The method may use the said optical source associated to the camera as alow coherent source to drive a low coherence interferometer implementedin the adapter.

The method may use phase shifting interferometry to produce at leastthree interference images for three phase shifts and where an enface OCTimage from the object is assembled from the at least three steps andwhere each step for phase shifting and the switch on of light from thesaid optical source are controlled by pressing the shutter button.

The method may use a digital colour camera with m sets of pixels witheach set sensitive to a given colour band to generate simultaneous m OCTinformation sets using each set of pixels as part of a distinct OCTchannel.

The method may use a two arms low coherence interferometer and where theoptical path difference between the lengths of the two arms can beadjusted independently for each of the m colour bands.

The method may use a phase shifting interferometry method to recover OCTinformation implemented in one step using the m sets of pixels in thephotodetector array.

In the method there may be m=3 spectral bands, r, g and b of centralwavelengths λ_(r), λ_(g), λ_(b) and signals delivered by each colourchannel in the camera are used to sense the OPD corresponding to thatrespective spectral band and

where the three OPD values are adjusted as 0 λ_(i), λ_(j)/3 and 2λ_(s)/3where i, j and s could be any set of permutations of r,g,b and wherethree interference images are generated by the said colour sensor array,one for each band r, g, b, with I_(r), I_(g), and I_(b), the intensityof the photodetected signal provided by each colour pixel and where aC-scan OCT image is assembled for each pixel in the C-scan image usingthe values of the same pixel in the three interference r, g, b imagesevaluated as: s=√{square root over((I_(r)−I_(g))²+(I_(g)−I_(b))²+(I_(r)−I_(b))²)}{square root over((I_(r)−I_(g))²+(I_(g)−I_(b))²+(I_(r)−I_(b))²)}{square root over((I_(r)−I_(g))²+(I_(g)−I_(b))²+(I_(r)−I_(b))²)}, where such OCT image isgenerated after pressing the said shutter button once.

In the method with m=3 spectral bands, r, g and b have centralwavelengths λ_(r), λ_(g), λ_(b), and where the signals delivered by eachcolour channel in the camera are used to sense the OPD corresponding tothat respective spectral band and

where at the first press of the said shutter button an optical pathdifference between each reference path length and the object path lengthis set at zero, the three channels collecting intensities I_(1p), withp=r,g,b,where at the second press of the shutter button the OPD values are setat λ_(r)/3 in the r reference path, λ_(g)/3 in the g reference path andof λ_(b)/3 in the b reference path and intensities I_(2p), with p=r,g,bare acquiredand where at the third press of the shutter button OPD values are set at2λ_(r)/3 in the r reference path, 2λ_(g)/3 in the g reference path andat 2λ_(b)/3 in the b reference path and intensities I_(3p) are acquired,with p=r,g,b, and where three C-scan OCT image of s_(p)=√{square rootover ((I_(1p)−I_(2p))²+(I_(1p)−I_(3p))²+(I_(2p)−I_(3p))²)}{square rootover ((I_(1p)−I_(2p))²+(I_(1p)−I_(3p))²+(I_(2p)−I_(3p))²)}{square rootover ((I_(1p)−I_(2p))²+(I_(1p)−I_(3p))²+(I_(2p)−I_(3p))²)} on each pixelwith p=r, g, b are assembled for each colour r, g, b in the said sensorfrom the three interference images acquired for the three presses of theshutter button.

The adapter may implement spectral decomposition of the light outputfrom the said low coherence interferometer and where the spectrumdispersed by spectral decomposition is read by the photo detector arrayin the said digital camera to produce by its Fourier transformation, areflectivity profile in depth through the said object at the press ofthe shutter of the said digital camera.

The method may use m reflectivity profiles generated by each set ofcolour pixels.

The method may use the output of the said low coherence interferometerspectrally separated in the said m bands which are angularly diverted atdifferent angles of incidence before being subject to spectraldecomposition, where the angles are adjusted in such a way that the raysof central wavelength of all three bands after spectral decompositionare angularly dispersed along a substantial similar direction to coverthe same set of pixels in the said photodetector array to be used todeliver the m OCT reflectivity profiles.

Light from a low coherent source may be conditioned to project a lightline on the object along an object lateral direction and N pixels in the1st direction of the said photodetector array in the digital camera areused to sense the lateral distribution of object reflectivity along theobject lateral direction while M pixels along the 2nd direction of thephotodetector array in the digital camera are used for the saidoperation of spectral decomposition to produce the said reflectivityprofile for each pixel up to N in the line along the 1^(st) direction togenerate m B-scan images of N by M pixels which map object lateraldirection by depth respectively.

The said low coherent source may be the flash source of the same digitalcolour camera, or the IR beam, or any external flash or pulse sourcewhere the flash time length can be independently adjusted from theintegration time of the sensor 3 (3′) in the camera 1 (1′).Alternatively, the adapter may make use of a CW optical source when manyframes are acquired.

An alternative method of high resolution imaging of an object based on atwo beams low coherence interferometer, under illumination from a lowcoherent source, of an object beam being sent to the object through theinterferometer to collect reflectivity of the object and the other areference beam, and where the interferometer has means to adjust theoptical path difference of the path lengths utilised by the object andreference beams and is terminated on a 50/50 splitter which outputs a1^(st) object beam and a 1^(st) reference beam, a 2^(nd) object beam anda 2^(nd) reference beam and where the interference signals from the1^(st) object and 1^(st) reference beams is in anti-phase with theinterference signal from the 2^(nd) object and the 2^(nd) reference beamand where the set of 1^(st) object and 1^(st) reference beams sufferspectral decomposition which is analysed by a 1^(st) digital camera andthe set of the 2^(nd) object and 2^(nd) reference beams suffer spectraldecomposition which is analysed by a 2^(nd) digital camera and where thecamera signals are deducted in a balance detection configuration toenhance the signal corresponding to the modulation of the spectraldecomposition and where the amount of overlap of the 1^(st) object beamand 1^(st) reference beam and of the 2^(nd) object beam and 2^(nd)reference beam is adjustable before spectral decomposition to producehigher strength of modulation of the spectral decomposition for one signof the optical path difference than for the other sign of the opticalpath difference in the interferometer.

In addition, confocal signals microscopy can be implemented as describedabove, by using the stray signals associated with diffraction ordispersion, to enable a dual simultaneous measurement or imagingtechnique, to produce combined signals OCT/CM for microscopy or OCT/SLOwhen imaging the retina. In this case, the method is to balance thespectral interferometry signals and sum the confocal stray signals. Thestray signals represent signals proportional to the intensity of theobject incident beam to the dispersion component.

The low coherent source may be a flash source associated to one or bothof the said digital cameras.

5. CONCLUDING REMARKS

It should be obvious for those skilled in the art that otherimplementations are possible. For instance, light from the flash lamps 4and from IR beam source 6 in the embodiments in FIGS. 1, 2, 4 and 6could be sent directly to the object 100 and not via optical splitters,such as 25.

Similarly, it should be obvious for those skilled in the art that lightfrom the flash lamps 4, 4′ and from IR beams 6 and 6′ in embodimentsusing two cameras, such as that disclosed in FIG. 5, could be sentdirectly to the object 100 and not via optical splitters, such as 25.

It should be obvious for those skilled in the art that steps in the OPDcould equally be introduced in the object path to achieve the samefunctionality as that presented here applying changes to the referencepath only.

It should also be obvious for those skilled in the art that the novelmethods disclosed here are applicable if a separate optical source isused, not in the same case (box) as that containing the sensor. Highperformance low cost detached photographic flashes, TTL controlled existand they could be employed similarly according to the disclosure. Also,it should be obvious for those skilled in the art that the novel methodsdisclosed here are applicable in cases using professional black andwhite cameras or professional colour cameras, or cameras which have morethan c=3 colour sensors cameras.

It should also be obvious that to avoid reflections from differentconstitutive elements, some may be eliminated from the embodimentspresented without departing from the scope of the invention. Also, wherelenses or microscope objectives were mentioned, they could be replacedby reflective converging elements, such as spherical or parabolicmirrors.

1. A camera adapter, for transforming a camera device having a housingcontaining a camera into an imaging instrument of an object, where thecamera in the camera device has at least an optical illumination sourcecreating excitation light, a photodetector array sensor behind an entry,a shutter release and a memory, wherein the camera adapter is adapted tobe placed between the camera device and the object and comprises: ahousing removable frame having securing fittings to hold the cameradevice securely in place, which housing removable frame comprises: afirst light output to transfer light to the object, a second lightoutput placed on the adapter in front of the commercial camera housingdevice for directing light from the adapter onto the photodetectorarray, at least a light input for accepting excitation light from the atleast an optical illumination source of the commercial camera housingdevice, means for directing the excitation light from the at least onelight input towards the first light output an object interface fordirecting light from the object into the second light output, so thatthe camera device is employed to collect an image of the object via theadapter into the memory of the camera device.
 2. Camera adapteraccording to claim 1, where the object interface is equipped with atleast an element out of the group of deflecting mirrors, beamsplittersand focusing elements out of the group of lenses and curved mirrors. 3.Camera adapter according to claim 1, where the means for directingexcitation light employ at least an element out of the group ofdeflecting mirrors and beamsplitters.
 4. Camera adapter according toclaim 1, where the means for directing excitation light deploy lightoff-axis to the light output
 1. 5. Camera adapter according to claim 1,where the means for directing excitation light are equipped with atleast one element of the group of: pinholes, wavelength filters,polarisers, waveplates, attenuators, converging and diverging elementsto adapt the divergence of the beam of light delivered by the at leastan optical illumination source to the size of the object illuminatedarea.
 6. Camera adapter according to claim 5, where when the means fordirecting excitation light contains at least an element of the group ofwaveplate and polariser, the interface optics contains a polarisationrejection analyser equipped with at least one of the following:waveplate and polariser to reduce stray reflections obscuring the objectexamined.
 7. Camera adapter according to claim 1, where the object isthe retina of a human or animal eye and where the adapter transforms thecamera device into a fundus imaging system, and where the focusingmeans, together with the focusing of the eye anterior chamber of theeye, form an image of the retina on the photodetector array of thecommercial camera housing device.
 8. Camera adapter according to claim1, where the camera device is equipped with two optical illuminationsources, an infrared light to guide camera autofocus and a visible lightfor flooding the object in the process of image taking, a camerafocusing element placed at the entry, autofocus means and a displayscreen for the image collected where the adapter has two light inputs,one for each illumination source and where the means for directingexcitation light, superpose the light from both light inputs into thesame beam directed towards the first light output.
 9. Camera adapteraccording to claim 8, where the adapter transforms the camera deviceinto a fundus imaging system, where the focusing means together with thecamera focusing element and together with the focusing of the eyeanterior chamber of the eye, form an image of the retina on thephotodetector array of the commercial camera housing device.
 10. Cameraadapter according to claim 1, equipped with an auxiliary illuminationsource directing light towards the means for directing the excitationlight.
 11. Camera adapter according to claim 1, where the photodetectorarray of the camera device is a colour sensor with three coloursensitivities in spectral windows r, g, b and where the means fordirecting excitation light supplementary contains one to three opticalfilters centred on the maximum of sensitivity within the spectralwindows r, g, b.
 12. Camera adapter according to claim 1 whichsupplementary contains interchangeable filters placed in the path of theexcitation light, a synchronous device, which is triggered by theemission of light by the commercial camera housing device that acts uponsequential change of optical filters.
 13. Camera adapter according toclaim 12 where the synchronous device is toggled by the shutter of thecommercial camera housing device to change a filter at a time, or whenthe camera is equipped with a repetitive collection function of images,to change several filters in sequence.
 14. A camera device having acamera adapter fitted, the camera device comprising: a housing; a cameracomprising at least an optical illumination source creating excitationlight, a photodetector array sensor behind an entry, a shutter releaseand a memory, wherein the camera adapter is placed between the cameradevice and the object and comprises: a housing removable frame havingsecuring fittings to hold the camera device securely in place, whichhousing removable frame comprises: a first light output to transferlight to the object, a second light output placed on the adapter infront of the commercial camera housing device for directing light fromthe adapter onto the photodetector array, at least a light input foraccepting excitation light from the at least an optical illuminationsource of the commercial camera housing device, means for directing theexcitation light from the at least one light input towards the firstlight output an object interface for directing light from the objectinto the second light output, so that the camera device is employed tocollect an image of the object via the adapter into the memory of thecamera device.
 15. Camera adapter according to claim 14, where theobject is tissue, such as skin or biopsied tissue, or a transparentmaterial of a human or animal eye and wherein: the adapter is arrangedto transform the camera device into a microscope imaging system, and thefocusing means are used to form an image of the object on thephotodetector array of the commercial camera housing device.
 16. Cameraadapter according to claim 15, where the camera device supplementarycontains a camera focusing element at the entry, and where the adaptertransforms the commercial camera housing device into a microscopeimaging system, where the focusing means together with the camerafocusing element form an image of the object on the photodetector arrayof the camera device.
 17. Method of investigation of an object, whichuses a camera device and an adapter, where the camera device having ahousing containing a camera, where the camera in the camera device hasat least an optical illumination source creating excitation light, aphotodetector array sensor behind an entry, a shutter release and amemory the adapter comprises: a housing removable frame having securingfittings to hold the camera device, securely in place, which housingcomprises a first light output to transfer light to the object, a secondlight output for directing light from the adapter onto the photodetectorarray, at least a light input for accepting excitation light from the atleast an optical illumination source of the commercial camera housingdevice, means for directing the excitation light from the at least onelight input towards the first light output, an object interface fordirecting light from the object into the second light output, the methodcomprising positioning the camera device inside the adapter in such away as: (i) the light input of the adapter collects excitation lightfrom the at least one illumination source of the camera and (ii) thesecond light output fits the entry to the camera, wherein the methodcomprising operating the camera part of the camera device together withthe adapter to: (i) spatially adjust the location of the camera deviceand adapter in front of the object by monitoring the camera display; and(ii) perform focusing on the object through the adapter and (iii)acquire an image of the object on the memory of the camera by pressingthe shutter of the commercial camera housing device.
 18. Method ofinvestigation of an object according to claim 17, where when the camerais equipped with a camera focusing element at the entry, the methodcomprising operating the camera part of the camera device together withthe adapter to supplementary perform focusing on the object through theadapter using the autofocus of the camera.
 19. Method of investigationof an object according to claim 17, where excitation light is added froman optical source attached or placed inside the adapter.
 20. Method ofinvestigation of an object according to claim 17, where the adapter isequipped with optical filters for the excitation light, which arechanged via a synchronous circuit under the control of the excitationlight and where for each press of the shutter of the camera, a filter ischanged inside the adapter when light from the excitation light isdetected by the synchronous circuit and the images so collected for eachfilter are downloaded from the memory into a computer or sent wirelesslyto a computer where they are combined to perform spectroscopic analysisof the object.
 21. Method of investigation of an object according toclaim 17, where when the camera is equipped with a display screen,adjustment of internal elements in the adapter such as focusing meansand means for directing excitation light are guided by the displayscreen of the camera in order to achieve maximum brightness, maximumsharpness and minimisation of stray reflections in the image.